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Geotag Everywhere with Fire Eagle Ben Ward A note from the editors: Since this article was written Yahoo! has retired the Fire Eagle service. Location, they say, is everywhere. Everyone has one, all of the time. But on the web, it’s taken until this year to see the emergence of location in the applications we use and build. The possibilities are broad. Increasingly, mobile phones provide SDKs to approximate your location wherever you are, browser extensions such as Loki and Mozilla’s Geode provide browser-level APIs to establish your location from the proximity of wireless networks to your laptop. Yahoo’s Brickhouse group launched Fire Eagle, an ambitious location broker enabling people to take their location from any of these devices or sources, and provide it to a plethora of web services. It enables you to take the location information that only your iPhone knows about and use it anywhere on the web. That said, this is still a time of location as an emerging technology. Fire Eagle stores your location on the web (protected by application-specific access controls), but to try and give an idea of how useful and powerful your location can be — regardless of the services you use now — today’s 24ways is going to build a bookmarklet to call up your location on demand, in any web application. Location Support on the Web Over the past year, the number of applications implementing location features has increased dramatically. Plazes and Brightkite are both full featured social networks based around where you are, whilst Pownce rolled in Fire Eagle support to allow geotagging of all the content you post to their microblogging service. Dipity’s beautiful timeline shows for you moving from place to place and Six Apart’s activity stream for Movable Type started exposing your movements. The number of services that hook into Fire Eagle will increase as location awareness spreads through the developer community, but you can use your location on other sites indirectly too. Consider Flickr. Now world renowned for their incredible mapping and places features, geotagging on Flickr started out as a grassroots extension of regular tagging. That same technique can be used to start rolling geotagging in any publishing platform you come across, for any kind of content. Machine-tags (geo:lat= and geo:lon=) and the adr and geo microformats can be used to enhance anything you write with location information. A crash course in avian inflammability Fire Eagle is a location store. A broker between services and devices which provide location and those which consume it. It’s a switchboard that controls which pieces of your location different applications can see and use, and keeps hidden anything you want kept private. A blog widget that displays your current location in public can be restricted to display just your current city, whilst a service that provides you with a list of the nearest ATMs will operate better with a precise street address. Even if your iPhone tells Fire Eagle exactly where you are, consuming applications only see what you want them to see. That’s important for users to realise that they’re in control, but also important for application developers to remember that you cannot rely on having super-accurate information available all the time. You need to build location aware applications which degrade gracefully, because users will provide fuzzier information — either through choice, or through less accurate sources. Application specific permissions are controlled through an OAuth API. Each application has a unique key, used to request a second, user-specific key that permits access to that user’s information. You store that user key and it remains valid until such a time as the user revokes your application’s access. Unlike with passwords, these keys are unique per application, so revoking the access rights of one application doesn’t break all the others. Building your first Fire Eagle app; Geomarklet Fire Eagle’s developer documentation can take you through examples of writing simple applications using server side technologies (PHP, Python). Here, we’re going to write a client-side bookmarklet to make your location available in every site you use. It’s designed to fast-track the experience of having location available everywhere on web, and show you how that can be really handy. Hopefully, this will set you thinking about how location can enhance the new applications you build in 2009. An oddity of bookmarklets Bookmarklets (or ‘favlets’, for those of an MSIE persuasion) are a strange environment to program in. Critically, you have no persistent storage available. As such, using token-auth APIs in a static environment requires you to build you application in a slightly strange way; authing yourself in advance and then hardcoding the keys into your script. Get started Before you do anything else, go to http://fireeagle.com and log in, get set up if you need to and by all means take a look around. Take a look at the mobile updaters section of the application gallery and perhaps pick out an app that will update Fire Eagle from your phone or laptop. Once that’s done, you need to register for an application key in the developer section. Head straight to /developer/create and complete the form. Since you’re building a standalone application, choose ‘Auth for desktop applications’ (rather than web applications), and select that you’ll be ‘accessing location’, not updating. At the end of this process, you’ll have two application keys, a ‘Consumer Key’ and a ‘Consumer Secret’, which look like these: Consumer Key luKrM9U1pMnu Consumer Secret ZZl9YXXoJX5KLiKyVrMZffNEaBnxnd6M These keys combined allow your application to make requests to Fire Eagle. Next up, you need to auth yourself; granting your new application permission to use your location. Because bookmarklets don’t have local storage, you can’t integrate the auth process into the bookmarklet itself — it would have no way of storing the returned key. Instead, I’ve put together a simple web frontend through which you can auth with your application. Head to Auth me, Amadeus!, enter the application keys you just generated and hit ‘Authorize with Fire Eagle’. You’ll be taken to the Fire Eagle website, just as in regular Fire Eagle applications, and after granting access to your app, be redirected back to Amadeus which will provide you your user tokens. These tokens are used in subsequent requests to read your location. And, skip to the end… The process of building the bookmarklet, making requests to Fire Eagle, rendering it to the page and so forth follows, but if you’re the impatient type, you might like to try this out right now. Take your four API keys from above, and drag the following link to your Bookmarks Toolbar; it contains all the code described below. Before you can use it, you need to edit in your own API keys. Open your browser’s bookmark editor and where you find text like ‘YOUR_CONSUMER_KEY_HERE’, swap in the corresponding key you just generated. Get Location Bookmarklet Basics To start on the bookmarklet code, set out a basic JavaScript module-pattern structure: var Geomarklet = function() { return ({ callback: function(json) {}, run: function() {} }); }; Geomarklet.run(); Next we’ll add the keys obtained in the setup step, and also some basic Fire Eagle support objects: var Geomarklet = function() { var Keys = { consumer_key: 'IuKrJUHU1pMnu', consumer_secret: 'ZZl9YXXoJX5KLiKyVEERTfNEaBnxnd6M', user_token: 'xxxxxxxxxxxx', user_secret: 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx' }; var LocationDetail = { EXACT: 0, POSTAL: 1, NEIGHBORHOOD: 2, CITY: 3, REGION: 4, STATE: 5, COUNTRY: 6 }; var index_offset; return ({ callback: function(json) {}, run: function() {} }); }; Geomarklet.run(); The Location Hierarchy A successful Fire Eagle query returns an object called the ‘location hierarchy’. Depending on the level of detail shared, the index of a particular piece of information in the array will vary. The LocationDetail object maps the array indices of each level in the hierarchy to something comprehensible, whilst the index_offset variable is an adjustment based on the detail of the result returned. The location hierarchy object looks like this, providing a granular breakdown of a location, in human consumable and machine-friendly forms. "user": { "location_hierarchy": [{ "level": 0, "level_name": "exact", "name": "707 19th St, San Francisco, CA", "normal_name": "94123", "geometry": { "type": "Point", "coordinates": [ - 0.2347530752, 67.232323] }, "label": null, "best_guess": true, "id": , "located_at": "2008-12-18T00:49:58-08:00", "query": "q=707%2019th%20Street,%20Sf" }, { "level": 1, "level_name": "postal", "name": "San Francisco, CA 94114", "normal_name": "12345", "woeid": , "place_id": "", "geometry": { "type": "Polygon", "coordinates": [], "bbox": [] }, "label": null, "best_guess": false, "id": 59358791, "located_at": "2008-12-18T00:49:58-08:00" }, { "level": 2, "level_name": "neighborhood", "name": "The Mission, San Francisco, CA", "normal_name": "The Mission", "woeid": 23512048, "place_id": "Y12JWsKbApmnSQpbQg", "geometry": { "type": "Polygon", "coordinates": [], "bbox": [] }, "label": null, "best_guess": false, "id": 59358801, "located_at": "2008-12-18T00:49:58-08:00" }, } In this case the first object has a level of 0, so the index_offset is also 0. Prerequisites To query Fire Eagle we call in some existing libraries to handle the OAuth layer and the Fire Eagle API call. Your bookmarklet will need to add the following scripts into the page: The SHA1 encryption algorithm The OAuth wrapper An extension for the OAuth wrapper The Fire Eagle wrapper itself When the bookmarklet is first run, we’ll insert these scripts into the document. We’re also inserting a stylesheet to dress up the UI that will be generated. If you want to follow along any of the more mundane parts of the bookmarklet, you can download the full source code. Rendering This bookmarklet can be extended to support any formatting of your location you like, but for sake of example I’m going to build three common formatters that you’ll find useful for common location scenarios: Sites which already ask for your location; and in publishing systems that accept tags or HTML mark-up. All the rendering functions are items in a renderers object, so they can be iterated through easily, making it trivial to add new formatting functions as your find new use cases (just add another function to the object). var renderers = { geotag: function(user) { if(LocationDetail.EXACT !== index_offset) { return false; } else { var coords = user.location_hierarchy[LocationDetail.EXACT].geometry.coordinates; return "geo:lat=" + coords[0] + ", geo:lon=" + coords[1]; } }, city: function(user) { if(LocationDetail.CITY < index_offset) { return false; } else { return user.location_hierarchy[LocationDetail.CITY - index_offset].name; } } You should always fail gracefully, and in line with catering to users who choose not to share their location precisely, always check that the location has been returned at the level you require. Geotags are expected to be precise, so if an exact location is unavailable, returning false will tell the rendering aspect of the bookmarklet to ignore the function altogether. These first two are quite simple, geotag returns geo:lat=-0.2347530752, geo:lon=67.232323 and city returns San Francisco, CA. This final renderer creates a chunk of HTML using the adr and geo microformats, using all available aspects of the location hierarchy, and can be used to geotag any content you write on your blog or in comments: html: function(user) { var geostring = ''; var adrstring = ''; var adr = []; adr.push('<p class="adr">'); // city if(LocationDetail.CITY >= index_offset) { adr.push( '\n <span class="locality">' + user.location_hierarchy[LocationDetail.CITY-index_offset].normal_name + '</span>,' ); } // county if(LocationDetail.REGION >= index_offset) { adr.push( '\n <span class="region">' + user.location_hierarchy[LocationDetail.REGION-index_offset].normal_name + '</span>,' ); } // locality if(LocationDetail.STATE >= index_offset) { adr.push( '\n <span class="region">' + user.location_hierarchy[LocationDetail.STATE-index_offset].normal_name + '</span>,' ); } // country if(LocationDetail.COUNTRY >= index_offset) { adr.push( '\n <span class="country-name">' + user.location_hierarchy[LocationDetail.COUNTRY-index_offset].normal_name + '</span>' ); } // postal if(LocationDetail.POSTAL >= index_offset) { adr.push( '\n <span class="postal-code">' + user.location_hierarchy[LocationDetail.POSTAL-index_offset].normal_name + '</span>,' ); } adr.push('\n</p>\n'); adrstring = adr.join(''); if(LocationDetail.EXACT === index_offset) { var coords = user.location_hierarchy[LocationDetail.EXACT].geometry.coordinates; geostring = '<p class="geo">' +'\n <span class="latitude">' + coords[0] + '</span>;' + '\n <span class="longitude">' + coords[1] + '</span>\n</p>\n'; } return (adrstring + geostring); } Here we check the availability of every level of location and build it into the adr and geo patterns as appropriate. Just as for the geotag function, if there’s no exact location the geo markup won’t be returned. Finally, there’s a rendering method which creates a container for all this data, renders all the applicable location formats and then displays them in the page for a user to copy and paste. You can throw this together with DOM methods and some simple styling, or roll in some components from YUI or JQuery to handle drawing full featured overlays. You can see this simple implementation for rendering in the full source code. Make the call With a framework in place to render Fire Eagle’s location hierarchy, the only thing that remains is to actually request your location. Having already authed through Amadeus earlier, that’s as simple as instantiating the Fire Eagle JavaScript wrapper and making a single function call. It’s a big deal that whilst a lot of new technologies like OAuth add some complexity and require new knowledge to work with, APIs like Fire Eagle are really very simple indeed. return { run: function() { insert_prerequisites(); setTimeout( function() { var fe = new FireEagle( Keys.consumer_key, Keys.consumer_secret, Keys.user_token, Keys.user_secret ); var script = document.createElement('script'); script.type = 'text/javascript'; script.src = fe.getUserUrl( FireEagle.RESPONSE_FORMAT.json, 'Geomarklet.callback' ); document.body.appendChild(script); }, 2000 ); }, callback: function(json) { if(json.rsp && 'fail' == json.rsp.stat) { alert('Error ' + json.rsp.code + ": " + json.rsp.message); } else { index_offset = json.user.location_hierarchy[0].level; draw_selector(json); } } }; We first insert the prerequisite scripts required for the Fire Eagle request to function, and to prevent trying to instantiate the FireEagle object before it’s been loaded over the wire, the remaining instantiation and request is wrapped inside a setTimeout delay. We then create the request URL, referencing the Geomarklet.callback callback function and then append the script to the document body — allowing a cross-domain request. The callback itself is quite simple. Check for the presence and value of rsp.status to test for errors, and display them as required. If the request is successful set the index_offset — to adjust for the granularity of the location hierarchy — and then pass the object to the renderer. The result? When Geomarklet.run() is called, your location from Fire Eagle is read, and each renderer displayed on the page in an easily copy and pasteable form, ready to be used however you need. Deploy The final step is to convert this code into a long string for use as a bookmarklet. Easiest for Mac users is the JavaScript bundle in TextMate — choose Bundles: JavaScript: Copy as Bookmarklet to Clipboard. Then create a new ‘Get Location’ bookmark in your browser of choice and paste in. Those without TextMate can shrink their code down into a single line by first running their code through the JSLint tool (to ensure the code is free from errors and has all the required semi-colons) and then use a find-and-replace tool to remove line breaks from your code (or even run your code through JSMin to shrink it down). With the bookmarklet created and added to your bookmarks bar, you can now call up your location on any page at all. Get a feel for a web where your location is just another reliable part of the browsing experience. Where next? So, the Geomarklet you’ve been guided through is a pretty simple premise and pretty simple output. But from this base you can start to extend: Add code that will insert each of the location renderings directly into form fields, perhaps, or how about site-specific handlers to add your location tags into the correct form field in Wordpress or Tumblr? Paste in your current location to Google Maps? Or Flickr? Geomarklet gives you a base to start experimenting with location on your own pages and the sites you browse daily. The introduction of consumer accessible geo to the web is an adventure of discovery; not so much discovering new locations, but discovering location itself. b'\x02\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\xa3\x00\x00\x00\x1f\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\\\x00\x00\x00\x15\x00\x00\x00'
Unobtrusively Mapping Microformats with jQuery Simon Willison Microformats are everywhere. You can’t shake an electronic stick these days without accidentally poking a microformat-enabled site, and many developers use microformats as a matter of course. And why not? After all, why invent your own class names when you can re-use pre-defined ones that give your site extra functionality for free? Nevertheless, while it’s good to know that users of tools such as Tails and Operator will derive added value from your shiny semantics, it’s nice to be able to reuse that effort in your own code. We’re going to build a map of some of my favourite restaurants in Brighton. Fitting with the principles of unobtrusive JavaScript, we’ll start with a semantically marked up list of restaurants, then use JavaScript to add the map, look up the restaurant locations and plot them as markers. We’ll be using a couple of powerful tools. The first is jQuery, a JavaScript library that is ideally suited for unobtrusive scripting. jQuery allows us to manipulate elements on the page based on their CSS selector, which makes it easy to extract information from microformats. The second is Mapstraction, introduced here by Andrew Turner a few days ago. We’ll be using Google Maps in the background, but Mapstraction makes it easy to change to a different provider if we want to later. Getting Started We’ll start off with a simple collection of microformatted restaurant details, representing my seven favourite restaurants in Brighton. The full, unstyled list can be seen in restaurants-plain.html. Each restaurant listing looks like this: <li class="vcard"> <h3><a class="fn org url" href="http://www.riddleandfinns.co.uk/">Riddle & Finns</a></h3> <div class="adr"> <p class="street-address">12b Meeting House Lane</p> <p><span class="locality">Brighton</span>, <abbr class="country-name" title="United Kingdom">UK</abbr></p> <p class="postal-code">BN1 1HB</p> </div> <p>Telephone: <span class="tel">+44 (0)1273 323 008</span></p> <p>E-mail: <a href="mailto:info@riddleandfinns.co.uk" class="email">info@riddleandfinns.co.uk</a></p> </li> Since we’re dealing with a list of restaurants, each hCard is marked up inside a list item. Each restaurant is an organisation; we signify this by placing the classes fn and org on the element surrounding the restaurant’s name (according to the hCard spec, setting both fn and org to the same value signifies that the hCard represents an organisation rather than a person). The address information itself is contained within a div of class adr. Note that the HTML <address> element is not suitable here for two reasons: firstly, it is intended to mark up contact details for the current document rather than generic addresses; secondly, address is an inline element and as such cannot contain the paragraphs elements used here for the address information. A nice thing about microformats is that they provide us with automatic hooks for our styling. For the moment we’ll just tidy up the whitespace a bit; for more advanced style tips consult John Allsop’s guide from 24 ways 2006. .vcard p { margin: 0; } .adr { margin-bottom: 0.5em; } To plot the restaurants on a map we’ll need latitude and longitude for each one. We can find this out from their address using geocoding. Most mapping APIs include support for geocoding, which means we can pass the API an address and get back a latitude/longitude point. Mapstraction provides an abstraction layer around these APIs which can be included using the following script tag: <script type="text/javascript" src="http://mapstraction.com/src/mapstraction-geocode.js"></script> While we’re at it, let’s pull in the other external scripts we’ll be using: <script type="text/javascript" src="jquery-1.2.1.js"></script> <script src="http://maps.google.com/maps?file=api&v=2&key=YOUR_KEY" type="text/javascript"></script> <script type="text/javascript" src="http://mapstraction.com/src/mapstraction.js"></script> <script type="text/javascript" src="http://mapstraction.com/src/mapstraction-geocode.js"></script> That’s everything set up: let’s write some JavaScript! In jQuery, almost every operation starts with a call to the jQuery function. The function simulates method overloading to behave in different ways depending on the arguments passed to it. When writing unobtrusive JavaScript it’s important to set up code to execute when the page has loaded to the point that the DOM is available to be manipulated. To do this with jQuery, pass a callback function to the jQuery function itself: jQuery(function() { // This code will be executed when the DOM is ready }); Initialising the map The first thing we need to do is initialise our map. Mapstraction needs a div with an explicit width, height and ID to show it where to put the map. Our document doesn’t currently include this markup, but we can insert it with a single line of jQuery code: jQuery(function() { // First create a div to host the map var themap = jQuery('<div id="themap"></div>').css({ 'width': '90%', 'height': '400px' }).insertBefore('ul.restaurants'); }); While this is technically just a single line of JavaScript (with line-breaks added for readability) it’s actually doing quite a lot of work. Let’s break it down in to steps: var themap = jQuery('<div id="themap"></div>') Here’s jQuery’s method overloading in action: if you pass it a string that starts with a < it assumes that you wish to create a new HTML element. This provides us with a handy shortcut for the more verbose DOM equivalent: var themap = document.createElement('div'); themap.id = 'themap'; Next we want to apply some CSS rules to the element. jQuery supports chaining, which means we can continue to call methods on the object returned by jQuery or any of its methods: var themap = jQuery('<div id="themap"></div>').css({ 'width': '90%', 'height': '400px' }) Finally, we need to insert our new HTML element in to the page. jQuery provides a number of methods for element insertion, but in this case we want to position it directly before the <ul> we are using to contain our restaurants. jQuery’s insertBefore() method takes a CSS selector indicating an element already on the page and places the current jQuery selection directly before that element in the DOM. var themap = jQuery('<div id="themap"></div>').css({ 'width': '90%', 'height': '400px' }).insertBefore('ul.restaurants'); Finally, we need to initialise the map itself using Mapstraction. The Mapstraction constructor takes two arguments: the first is the ID of the element used to position the map; the second is the mapping provider to use (in this case google ): // Initialise the map var mapstraction = new Mapstraction('themap','google'); We want the map to appear centred on Brighton, so we’ll need to know the correct co-ordinates. We can use www.getlatlon.com to find both the co-ordinates and the initial map zoom level. // Show map centred on Brighton mapstraction.setCenterAndZoom( new LatLonPoint(50.82423734980143, -0.14007568359375), 15 // Zoom level appropriate for Brighton city centre ); We also want controls on the map to allow the user to zoom in and out and toggle between map and satellite view. mapstraction.addControls({ zoom: 'large', map_type: true }); Adding the markers It’s finally time to parse some microformats. Since we’re using hCard, the information we want is wrapped in elements with the class vcard. We can use jQuery’s CSS selector support to find them: var vcards = jQuery('.vcard'); Now that we’ve found them, we need to create a marker for each one in turn. Rather than using a regular JavaScript for loop, we can instead use jQuery’s each() method to execute a function against each of the hCards. jQuery('.vcard').each(function() { // Do something with the hCard }); Within the callback function, this is set to the current DOM element (in our case, the list item). If we want to call the magic jQuery methods on it we’ll need to wrap it in another call to jQuery: jQuery('.vcard').each(function() { var hcard = jQuery(this); }); The Google maps geocoder seems to work best if you pass it the street address and a postcode. We can extract these using CSS selectors: this time, we’ll use jQuery’s find() method which searches within the current jQuery selection: var streetaddress = hcard.find('.street-address').text(); var postcode = hcard.find('.postal-code').text(); The text() method extracts the text contents of the selected node, minus any HTML markup. We’ve got the address; now we need to geocode it. Mapstraction’s geocoding API requires us to first construct a MapstractionGeocoder, then use the geocode() method to pass it an address. Here’s the code outline: var geocoder = new MapstractionGeocoder(onComplete, 'google'); geocoder.geocode({'address': 'the address goes here'); The onComplete function is executed when the geocoding operation has been completed, and will be passed an object with the resulting point on the map. We just want to create a marker for the point: var geocoder = new MapstractionGeocoder(function(result) { var marker = new Marker(result.point); mapstraction.addMarker(marker); }, 'google'); For our purposes, joining the street address and postcode with a comma to create the address should suffice: geocoder.geocode({'address': streetaddress + ', ' + postcode}); There’s one last step: when the marker is clicked, we want to display details of the restaurant. We can do this with an info bubble, which can be configured by passing in a string of HTML. We’ll construct that HTML using jQuery’s html() method on our hcard object, which extracts the HTML contained within that DOM node as a string. var marker = new Marker(result.point); marker.setInfoBubble( '<div class="bubble">' + hcard.html() + '</div>' ); mapstraction.addMarker(marker); We’ve wrapped the bubble in a div with class bubble to make it easier to style. Google Maps can behave strangely if you don’t provide an explicit width for your info bubbles, so we’ll add that to our CSS now: .bubble { width: 300px; } That’s everything we need: let’s combine our code together: jQuery(function() { // First create a div to host the map var themap = jQuery('<div id="themap"></div>').css({ 'width': '90%', 'height': '400px' }).insertBefore('ul.restaurants'); // Now initialise the map var mapstraction = new Mapstraction('themap','google'); mapstraction.addControls({ zoom: 'large', map_type: true }); // Show map centred on Brighton mapstraction.setCenterAndZoom( new LatLonPoint(50.82423734980143, -0.14007568359375), 15 // Zoom level appropriate for Brighton city centre ); // Geocode each hcard and add a marker jQuery('.vcard').each(function() { var hcard = jQuery(this); var streetaddress = hcard.find('.street-address').text(); var postcode = hcard.find('.postal-code').text(); var geocoder = new MapstractionGeocoder(function(result) { var marker = new Marker(result.point); marker.setInfoBubble( '<div class="bubble">' + hcard.html() + '</div>' ); mapstraction.addMarker(marker); }, 'google'); geocoder.geocode({'address': streetaddress + ', ' + postcode}); }); }); Here’s the finished code. There’s one last shortcut we can add: jQuery provides the $ symbol as an alias for jQuery. We could just go through our code and replace every call to jQuery() with a call to $(), but this would cause incompatibilities if we ever attempted to use our script on a page that also includes the Prototype library. A more robust approach is to start our code with the following: jQuery(function($) { // Within this function, $ now refers to jQuery // ... }); jQuery cleverly passes itself as the first argument to any function registered to the DOM ready event, which means we can assign a local $ variable shortcut without affecting the $ symbol in the global scope. This makes it easy to use jQuery with other libraries. Limitations of Geocoding You may have noticed a discrepancy creep in to the last example: whereas my original list included seven restaurants, the geocoding example only shows five. This is because the Google Maps geocoder incorporates a rate limit: more than five lookups in a second and it starts returning error messages instead of regular results. In addition to this problem, geocoding itself is an inexact science: while UK postcodes generally get you down to the correct street, figuring out the exact point on the street from the provided address usually isn’t too accurate (although Google do a pretty good job). Finally, there’s the performance overhead. We’re making five geocoding requests to Google for every page served, even though the restaurants themselves aren’t likely to change location any time soon. Surely there’s a better way of doing this? Microformats to the rescue (again)! The geo microformat suggests simple classes for including latitude and longitude information in a page. We can add specific points for each restaurant using the following markup: <li class="vcard"> <h3 class="fn org">E-Kagen</h3> <div class="adr"> <p class="street-address">22-23 Sydney Street</p> <p><span class="locality">Brighton</span>, <abbr class="country-name" title="United Kingdom">UK</abbr></p> <p class="postal-code">BN1 4EN</p> </div> <p>Telephone: <span class="tel">+44 (0)1273 687 068</span></p> <p class="geo">Lat/Lon: <span class="latitude">50.827917</span>, <span class="longitude">-0.137764</span> </p> </li> As before, I used www.getlatlon.com to find the exact locations – I find satellite view is particularly useful for locating individual buildings. Latitudes and longitudes are great for machines but not so useful for human beings. We could hide them entirely with display: none, but I prefer to merely de-emphasise them (someone might want them for their GPS unit): .vcard .geo { margin-top: 0.5em; font-size: 0.85em; color: #ccc; } It’s probably a good idea to hide them completely when they’re displayed inside an info bubble: .bubble .geo { display: none; } We can extract the co-ordinates in the same way we extracted the address. Since we’re no longer geocoding anything our code becomes a lot simpler: $('.vcard').each(function() { var hcard = $(this); var latitude = hcard.find('.geo .latitude').text(); var longitude = hcard.find('.geo .longitude').text(); var marker = new Marker(new LatLonPoint(latitude, longitude)); marker.setInfoBubble( '<div class="bubble">' + hcard.html() + '</div>' ); mapstraction.addMarker(marker); }); And here’s the finished geo example. Further reading We’ve only scratched the surface of what’s possible with microformats, jQuery (or just regular JavaScript) and a bit of imagination. If this example has piqued your interest, the following links should give you some more food for thought. The hCard specification Notes on parsing hCards jQuery for JavaScript programmers – my extended tutorial on jQuery. Dann Webb’s Sumo – a full JavaScript library for parsing microformats, based around some clever metaprogramming techniques. Jeremy Keith’s Adactio Austin – the first place I saw using microformats to unobtrusively plot locations on a map. Makes clever use of hEvent as well. b"\x02\x00\x00\x00\x03\x00\x00\x00\x01\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'\x00\x00\x00\xa3\x00\x00\x00\x1f\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x06\x00\x00\x00\\\x00\x00\x00\x15\x00\x00\x00"
Front-End Code Reusability with CSS and JavaScript Trevor Morris Most web standards-based developers are more than familiar with creating their sites with semantic HTML with lots and lots of CSS. With each new page in a design, the CSS tends to grow and grow and more elements and styles are added. But CSS can be used to better effect. The idea of object-oriented CSS isn’t new. Nicole Sullivan has written a presentation on the subject and outlines two main concepts: separate structure and visual design; and separate container and content. Jeff Croft talks about Applying OOP Concepts to CSS: I can make a class of .box that defines some basic layout structure, and another class of .rounded that provides rounded corners, and classes of .wide and .narrow that define some widths, and then easily create boxes of varying widths and styles by assigning multiple classes to an element, without having to duplicate code in my CSS. This concept helps reduce CSS file size, allows for great flexibility, rapid building of similar content areas and means greater consistency throughout the entire design. You can also take this concept one step further and apply it to site behaviour with JavaScript. Build a versatile slideshow I will show you how to build multiple slideshows using jQuery, allowing varying levels of functionality which you may find on one site design. The code will be flexible enough to allow you to add previous/next links, image pagination and the ability to change the animation type. More importantly, it will allow you to apply any combination of these features. Image galleries are simply a list of images, so the obvious choice of marking the content up is to use a <ul>. Many designs, however, do not cater to non-JavaScript versions of the website, and thus don’t take in to account large multiple images. You could also simply hide all the other images in the list, apart from the first image. This method can waste bandwidth because the other images might be downloaded when they are never going to be seen. Taking this second concept — only showing one image — the only code you need to start your slideshow is an <img> tag. The other images can be loaded dynamically via either a per-page JavaScript array or via AJAX. The slideshow concept is built upon the very versatile Cycle jQuery Plugin and is structured in to another reusable jQuery plugin. Below is the HTML and JavaScript snippet needed to run every different type of slideshow I have mentioned above. <img src="path/to/image.jpg" alt="About the image" title="" height="250" width="400" class="slideshow"> <script type="text/javascript"> jQuery().ready(function($) { $('img.slideshow').slideShow({ images: ['1.jpg', '2.jpg', '3.jpg'] }); }); </script> Slideshow plugin If you’re not familiar with jQuery or how to write and author your own plugin there are plenty of articles to help you out. jQuery has a chainable interface and this is something your plugin must implement. This is easy to achieve, so your plugin simply returns the collection it is using: return this.each( function () {} }; Local Variables To keep the JavaScript clean and avoid any conflicts, you must set up any variables which are local to the plugin and should be used on each collection item. Defining all your variables at the top under one statement makes adding more and finding which variables are used easier. For other tips, conventions and improvements check out JSLint, the “JavaScript Code Quality Tool”. var $$, $div, $images, $arrows, $pager, id, selector, path, o, options, height, width, list = [], li = 0, parts = [], pi = 0, arrows = ['Previous', 'Next']; Cache jQuery Objects It is good practice to cache any calls made to jQuery. This reduces wasted DOM calls, can improve the speed of your JavaScript code and makes code more reusable. The following code snippet caches the current selected DOM element as a jQuery object using the variable name $$. Secondly, the plugin makes its settings available to the Metadata plugin‡ which is best practice within jQuery plugins. For each slideshow the plugin generates a <div> with a class of slideshow and a unique id. This is used to wrap the slideshow images, pagination and controls. The base path which is used for all the images in the slideshow is calculated based on the existing image which appears on the page. For example, if the path to the image on the page was /img/flowers/1.jpg the plugin would use the path /img/flowers/ to load the other images. $$ = $(this); o = $.metadata ? $.extend({}, settings, $$.metadata()) : settings; id = 'slideshow-' + (i++ + 1); $div = $('<div />').addClass('slideshow').attr('id', id); selector = '#' + id + ' '; path = $$.attr('src').replace(/[0-9]\.jpg/g, ''); options = {}; height = $$.height(); width = $$.width(); Note: the plugin uses conventions such as folder structure and numeric filenames. These conventions help with the reusable aspect of plugins and best practices. Build the Images The cycle plugin uses a list of images to create the slideshow. Because we chose to start with one image we must now build the list programmatically. This is a case of looping through the images which were added via the plugin options, building the appropriate HTML and appending the resulting <ul> to the DOM. $.each(o.images, function () { list[li++] = '<li>'; list[li++] = '<img src="' + path + this + '" height="' + height + '" width="' + width + '">'; list[li++] = '</li>'; }); $images = $('<ul />').addClass('cycle-images'); $images.append(list.join('')).appendTo($div); Although jQuery provides the append method it is much faster to create one really long string and append it to the DOM at the end. Update the Options Here are some of the options we’re making available by simply adding classes to the <img>. You can change the slideshow effect from the default fade to the sliding effect. By adding the class of stopped the slideshow will not auto-play and must be controlled via pagination or previous and next links. // different effect if ($$.is('.slide')) { options.fx = 'scrollHorz'; } // don't move by default if ($$.is('.stopped')) { options.timeout = 0; } If you are using the same set of images throughout a website you may wish to start on a different image on each page or section. This can be easily achieved by simply adding the appropriate starting class to the <img>. // based on the class name on the image if ($$.is('[class*=start-]')) { options.startingSlide = parseInt($$.attr('class').replace(/.*start-([0-9]+).*/g, "$1"), 10) - 1; } For example: <img src="/img/slideshow/3.jpg" alt="About the image" title="" height="250" width="400" class="slideshow start-3"> By default, and without JavaScript, the third image in this slideshow is shown. When the JavaScript is applied to the page the slideshow must know to start from the correct place, this is why the start class is required. You could capture the default image name and parse it to get the position, but only the default image needs to be numeric to work with this plugin (and could easily be changed in future). Therefore, this extra specifically defined option means the plugin is more tolerant. Previous/Next Links A common feature of slideshows is previous and next links enabling the user to manually progress the images. The Cycle plugin supports this functionality, but you must generate the markup yourself. Most people add these directly in the HTML but normally only support their behaviour when JavaScript is enabled. This goes against progressive enhancement. To keep with the best practice progress enhancement method the previous/next links should be generated with JavaScript. The follow snippet checks whether the slideshow requires the previous/next links, via the arrows class. It restricts the Cycle plugin to the specific slideshow using the selector we created at the top of the plugin. This means multiple slideshows can run on one page without conflicting each other. The code creates a <ul> using the arrows array we defined at the top of the plugin. It also adds a class to the slideshow container, meaning you can style different combinations of options in your CSS. // create the arrows if ($$.is('.arrows') && list.length > 1) { options.next = selector + '.next'; options.prev = selector + '.previous'; $arrows = $('<ul />').addClass('cycle-arrows'); $.each(arrows, function (i, val) { parts[pi++] = '<li class="' + val.toLowerCase() + '">'; parts[pi++] = '<a href="#' + val.toLowerCase() + '">'; parts[pi++] = '<span>' + val + '</span>'; parts[pi++] = '</a>'; parts[pi++] = '</li>'; }); $arrows.append(parts.join('')).appendTo($div); $div.addClass('has-cycle-arrows'); } The arrow array could be placed inside the plugin settings to allow for localisation. Pagination The Cycle plugin creates its own HTML for the pagination of the slideshow. All our plugin needs to do is create the list and selector to use. This snippet creates the pagination container and appends it to our specific slideshow container. It sets the Cycle plugin pager option, restricting it to the specific slideshow using the selector we created at the top of the plugin. Like the previous/next links, a class is added to the slideshow container allowing you to style the slideshow itself differently. // create the clickable pagination if ($$.is('.pagination') && list.length > 1) { options.pager = selector + '.cycle-pagination'; $pager = $('<ul />').addClass('cycle-pagination'); $pager.appendTo($div); $div.addClass('has-cycle-pagination'); } Note: the Cycle plugin creates a <ul> with anchors listed directly inside without the surrounding <li>. Unfortunately this is invalid markup but the code still works. Demos Well, that describes all the ins-and-outs of the plugin, but demos make it easier to understand! Viewing the source on the demo page shows some of the combinations you can create with a simple <img>, a few classes and some thought-out JavaScript. View the demos → Decide on defaults The slideshow plugin uses the exact same settings as the Cycle plugin, but some are explicitly set within the slideshow plugin when using the classes you have set. When deciding on what functionality is going to be controlled via this class method, be careful to choose your defaults wisely. If all slideshows should auto-play, don’t make this an option — make the option to stop the auto-play. Similarly, if every slideshow should have previous/next functionality make this the default and expose the ability to remove them with a class such as “no-pagination”. In the examples presented on this article I have used a class on each <img>. You can easily change this to anything you want and simply apply the plugin based on the jQuery selector required. Grab your images If you are using AJAX to load in your images, you can speed up development by deciding on and keeping to a folder structure and naming convention. There are two methods: basing the image path based on the current URL; or based on the src of the image. The first allows a different slideshow on each page, but in many instances a site will have a couple of sets of images and therefore the second method is probably preferred. Metadata ‡ A method which allows you to directly modify settings in certain plugins, which also uses the classes from your HTML already exists. This is a jQuery plugin called Metadata. This method allows for finer control over the plugin settings themselves. Some people, however, may dislike the syntax and prefer using normal classes, like above which when sprinkled with a bit more JavaScript allows you to control what you need to control. The takeaway Hopefully you have understood not only what goes in to a basic jQuery plugin but also learnt a new and powerful idea which you can apply to other areas of your website. The idea can also be applied to other common interfaces such as lightboxes or mapping services such as Google Maps — for example creating markers based on a list of places, each with different pin icons based the anchor class. b'\x02\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0e\x00\x00\x00\xa3\x00\x00\x00\x1f\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\\\x00\x00\x00\x15\x00\x00\x00'
Finding Your Way with Static Maps Drew McLellan Since the introduction of the Google Maps service in 2005, online maps have taken off in a way not really possible before the invention of slippy map interaction. Although quickly followed by a plethora of similar services from both commercial and non-commercial parties, Google’s first-mover advantage, and easy-to-use developer API saw Google Maps become pretty much the de facto mapping service. It’s now so easy to add a map to a web page, there’s no reason not to. Dropping an iframe map into your page is as simple as embedding a YouTube video. But there’s one crucial drawback to both the solution Google provides for you to drop into your page and the code developers typically implement themselves – they don’t work without JavaScript. A bit about JavaScript Back in October of this year, The Yahoo! Developer Network blog ran some tests to measure how many visitors to the Yahoo! home page didn’t have JavaScript available or enabled in their browser. It’s an interesting test when you consider that the audience for the Yahoo! home page (one of the most visited pages on the web) represents about as mainstream a sample as you’ll find. If there’s any such thing as an ‘average Web user’ then this is them. The results surprised me. It varied from region to region, but at most just two per cent of visitors didn’t have JavaScript running. To be honest, I was expecting it to be higher, but this quote from the article caught my attention: While the percentage of visitors with JavaScript disabled seems like a low number, keep in mind that small percentages of big numbers are also big numbers. That’s right, of course, and it got me thinking about what that two per cent means. For many sites, two per cent is the number of visitors using the Opera web browser, using IE6, or using Mobile Safari. So, although a small percentage of the total, users without JavaScript can’t just be forgotten about, and catering for them is at the very heart of how the web is supposed to work. Starting with content in HTML, we layer on presentation with CSS and then enhance interactivity with JavaScript. If anything fails along the way or the network craps out, or a browser just doesn’t support one of the technologies, the user still gets something they can work with. It’s progressive enhancement – also known as doing our jobs properly. Sorry, wasn’t this about maps? As I was saying, the default code Google provides, and the example code it gives to developers (which typically just gets followed ‘as is’) doesn’t account for users without JavaScript. No JavaScript, no content. When adding the ability to publish maps to our small content management system Perch, I didn’t want to provide a solution that only worked with JavaScript. I had to go looking for a way to provide maps without JavaScript, too. There’s a simple solution, fortunately, in the form of static map tiles. All the various slippy map services use a JavaScript interface on top of what are basically rendered map image tiles. Dragging the map loads in more image tiles in the direction you want to view. If you’ve used a slippy map on a slow connection, you’ll be familiar with seeing these tiles load in one by one. The Static Map API The good news is that these tiles (or tiles just like them) can be used as regular images on your site. Google has a Static Map API which not only gives you a handy interface to retrieve a tile for the exact area you need, but also allows you to place pins, and zoom and centre the tile so that the image looks just so. This means that you can create a static, non-JavaScript version of your slippy map’s initial (or ideal) state to load into your page as a regular image, and then have the JavaScript map hijack the image and make it slippy. Clearly, that’s not going to be a perfect solution for every map’s requirements. It doesn’t allow for panning, zooming or interrogation without JavaScript. However, for the majority of straightforward map uses online, a static map makes a great alternative for those visitors without JavaScript. Here’s the how Retrieving a static map tile is staggeringly easy – it’s just a case of forming a URL with the correct arguments and then using that as the src of an image tag. <img src="http://maps.google.com/maps/api/staticmap ?center=Bethlehem+Israel &zoom=5 &size=540x280 &maptype=satellite &markers=color:red|31.4211,35.1144 &sensor=false" width="540" height="280" alt="Map of Bethlehem, Israel" /> As you can see, there are a few key options that we pass along to the base URL. All of these should be familiar to anyone who’s worked with the JavaScript API. center determines the point on which the map is centred. This can be latitude and longitude values, or simply an address which is then geocoded. zoom sets the zoom level. size is the pixel dimensions of the image you require. maptype can be roadmap, satellite, terrain or hybrid. markers sets one or more pin locations. Markers can be labelled, have different colours, and so on – there’s quite a lot of control available. sensor states whether you are using a sensor to determine the user’s location. When just embedding a map in a web page, set this to false. There are many options, including plotting paths and setting the image format, which can all be found in the straightforward documentation. Adding to your page If you’ve worked with the JavaScript API, you’ll know that it needs a container element which you inject the map into: <div id="map"></div> All you need to do is put your static image inside that container: <div id="map"> <img src="http://maps.google.com/maps/api/staticmap[...]" /> </div> And then, in your JavaScript, find the image and remove it. For example, with jQuery you’d simply use: $('#map img').remove(); Why not use a <noscript> element around the image? You could, and that would certainly work fine for browsers that do not support JavaScript. What that won’t cover, however, is the situation where the browser has JavaScript support but, for whatever reason, the JavaScript doesn’t run. This could be due to network issues, an aggressive corporate firewall, or even just a bug in your code. So for that reason, we put the image in for all browsers that show images, and then remove it when the JavaScript is successfully running. See an example in action About rate limits The Google Static Map API limits the requests per site viewer – currently at one thousand distinct maps per day per viewer. So, for most sites you really don’t need to worry about the rate limit. Requests for the same tile aren’t normally counted, as the tile has already been generated and is cached. You can embed the images direct from Google and let it worry about the distribution and caching. In conclusion As you can see, adding a static map alongside your dynamic map for those users without JavaScript is very easy indeed. There may not be a huge percentage of web visitors browsing without JavaScript but, as we’ve seen, a small percentage of a big number is still a big number. When it’s so easy to add a static map, can you really justify not doing it? b'\x02\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\xa3\x00\x00\x00\x1f\x00\x00\x00\x01\x00\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0b\x00\x00\x00\\\x00\x00\x00\x15\x00\x00\x00'
Your jQuery: Now With 67% Less Suck Scott Kosman Fun fact: more websites are now using jQuery than Flash. jQuery is an amazing tool that’s made JavaScript accessible to developers and designers of all levels of experience. However, as Spiderman taught us, “with great power comes great responsibility.” The unfortunate downside to jQuery is that while it makes it easy to write JavaScript, it makes it easy to write really really f*&#ing bad JavaScript. Scripts that slow down page load, unresponsive user interfaces, and spaghetti code knotted so deep that it should come with a bottle of whiskey for the next sucker developer that has to work on it. This becomes more important for those of us who have yet to move into the magical fairy wonderland where none of our clients or users view our pages in Internet Explorer. The IE JavaScript engine moves at the speed of an advancing glacier compared to more modern browsers, so optimizing our code for performance takes on an even higher level of urgency. Thankfully, there are a few very simple things anyone can add into their jQuery workflow that can clear up a lot of basic problems. When undertaking code reviews, three of the areas where I consistently see the biggest problems are: inefficient selectors; poor event delegation; and clunky DOM manipulation. We’ll tackle all three of these and hopefully you’ll walk away with some new jQuery batarangs to toss around in your next project. Selector optimization Selector speed: fast or slow? Saying that the power behind jQuery comes from its ability to select DOM elements and act on them is like saying that Photoshop is a really good tool for selecting pixels on screen and making them change color – it’s a bit of a gross oversimplification, but the fact remains that jQuery gives us a ton of ways to choose which element or elements in a page we want to work with. However, a surprising number of web developers are unaware that all selectors are not created equal; in fact, it’s incredible just how drastic the performance difference can be between two selectors that, at first glance, appear nearly identical. For instance, consider these two ways of selecting all paragraph tags inside a <div> with an ID. $("#id p"); $("#id").find("p"); Would it surprise you to learn that the second way can be more than twice as fast as the first? Knowing which selectors outperform others (and why) is a pretty key building block in making sure your code runs well and doesn’t frustrate your users waiting for things to happen. There are many different ways to select elements using jQuery, but the most common ways can be basically broken down into five different methods. In order, roughly, from fastest to slowest, these are: $("#id"); This is without a doubt the fastest selector jQuery provides because it maps directly to the native document.getElementbyId() JavaScript method. If possible, the selectors listed below should be prefaced with an ID selector in conjunction with jQuery’s .find() method to limit the scope of the page that has to be searched (as in the $("#id").find("p") example shown above). $("p");, $("input");, $("form"); and so on Selecting elements by tag name is also fast, since it maps directly to the native document.getElementsByTagname() method. $(".class"); Selecting by class name is a little trickier. While still performing very well in modern browsers, it can cause some pretty significant slowdowns in IE8 and below. Why? IE9 was the first IE version to support the native document.getElementsByClassName() JavaScript method. Older browsers have to resort to using much slower DOM-scraping methods that can really impact performance. $("[attribute=value]"); There is no native JavaScript method for this selector to use, so the only way that jQuery can perform the search is by crawling the entire DOM looking for matches. Modern browsers that support the querySelectorAll() method will perform better in certain cases (Opera, especially, runs these searches much faster than any other browser) but, generally speaking, this type of selector is Slowey McSlowersons. $(":hidden"); Like attribute selectors, there is no native JavaScript method for this one to use. Pseudo-selectors can be painfully slow since the selector has to be run against every element in your search space. Again, modern browsers with querySelectorAll() will perform slightly better here, but try to avoid these if at all possible. If you must use one, try to limit the search space to a specific portion of the page: $("#list").find(":hidden"); But, hey, proof is in the performance testing, right? It just so happens that said proof is sitting right here. Be sure to notice the class selector numbers beside IE7 and 8 compared to other browsers and then wonder how the people on the IE team at Microsoft manage to sleep at night. Yikes. Chaining Almost all jQuery methods return a jQuery object. This means that when a method is run, its results are returned and you can continue executing more methods on them. Rather than writing out the same selector multiple times over, just making a selection once allows multiple actions to be run on it. Without chaining $("#object").addClass("active"); $("#object").css("color","#f0f"); $("#object").height(300); With chaining $("#object").addClass("active").css("color", "#f0f").height(300); This has the dual effect of making your code shorter and faster. Chained methods will be slightly faster than multiple methods made on a cached selector, and both ways will be much faster than multiple methods made on non-cached selectors. Wait… “cached selector”? What is this new devilry? Caching Another easy way to speed up your code that seems to be a mystery to developers is the idea of caching your selectors. Think of how many times you end up writing the same selector over and over again in any project. Every $(".element") selector has to search the entire DOM each time, regardless of whether or not that selector had been previously run. Running the selection once and then storing the results in a variable means that the DOM only has to be searched once. Once the results of a selector have been cached, you can do anything with them. First, run your search (here we’re selecting all of the <li> elements inside <ul id="blocks">): var blocks = $("#blocks").find("li"); Now, you can use the blocks variable wherever you want without having to search the DOM every time. $("#hideBlocks").click(function() { blocks.fadeOut(); }); $("#showBlocks").click(function() { blocks.fadeIn(); }); My advice? Any selector that gets run more than once should be cached. This jsperf test shows just how much faster a cached selector runs compared to a non-cached one (and even throws some chaining love in to boot). Event delegation Event listeners cost memory. In complex websites and apps it’s not uncommon to have a lot of event listeners floating around, and thankfully jQuery provides some really easy methods for handling event listeners efficiently through delegation. In a bit of an extreme example, imagine a situation where a 10×10 cell table needs to have an event listener on each cell; let’s say that clicking on a cell adds or removes a class that defines the cell’s background color. A typical way that this might be written (and something I’ve often seen during code reviews) is like so: $('table').find('td').click(function() { $(this).toggleClass('active'); }); jQuery 1.7 has provided us with a new event listener method, .on(). It acts as a utility that wraps all of jQuery’s previous event listeners into one convenient method, and the way you write it determines how it behaves. To rewrite the above .click() example using .on(), we’d simply do the following: $('table').find('td').on('click',function() { $(this).toggleClass('active'); }); Simple enough, right? Sure, but the problem here is that we’re still binding one hundred event listeners to our page, one to each individual table cell. A far better way to do things is to create one event listener on the table itself that listens for events inside it. Since the majority of events bubble up the DOM tree, we can bind a single event listener to one element (in this case, the <table>) and wait for events to bubble up from its children. The way to do this using the .on() method requires only one change from our code above: $('table').on('click','td',function() { $(this).toggleClass('active'); }); All we’ve done is moved the td selector to an argument inside the .on() method. Providing a selector to .on() switches it into delegation mode, and the event is only fired for descendants of the bound element (table) that match the selector (td). With that one simple change, we’ve gone from having to bind one hundred event listeners to just one. You might think that the browser having to do one hundred times less work would be a good thing and you’d be completely right. The difference between the two examples above is staggering. (Note that if your site is using a version of jQuery earlier than 1.7, you can accomplish the very same thing using the .delegate() method. The syntax of how you write the function differs slightly; if you’ve never used it before, it’s worth checking the API docs for that page to see how it works.) DOM manipulation jQuery makes it very easy to manipulate the DOM. It’s trivial to create new nodes, insert them, remove other ones, move things around, and so on. While the code to do this is simple to write, every time the DOM is manipulated, the browser has to repaint and reflow content which can be extremely costly. This is no more evident than in a long loop, whether it be a standard for() loop, while() loop, or jQuery $.each() loop. In this case, let’s say we’ve just received an array full of image URLs from a database or Ajax call or wherever, and we want to put all of those images in an unordered list. Commonly, you’ll see code like this to pull this off: var arr = [reallyLongArrayOfImageURLs]; $.each(arr, function(count, item) { var newImg = '<li><img src="'+item+'"></li>'; $('#imgList').append(newImg); }); There are a couple of problems with this. For one (which you should have already noticed if you’ve read the earlier part of this article), we’re making the $("#imgList") selection once for each iteration of our loop. The other problem here is that each time the loop iterates, it’s adding a new <li> to the DOM. Each of those insertions is going to be costly, and if our array is quite large then this could lead to a massive slowdown or even the dreaded ‘A script is causing this page to run slowly’ warning. var arr = [reallyLongArrayOfImageURLs], tmp = ''; $.each(arr, function(count, item) { tmp += '<li><img src="'+item+'"></li>'; }); $('#imgList').append(tmp); All we’ve done here is create a tmp variable that each <li> is added to as it’s created. Once our loop has finished iterating, that tmp variable will contain all of our list items in memory, and can be appended to our <ul> all in one go. Browsers work much faster when working with objects in memory rather than on screen, so this is a much faster, more CPU-cycle-friendly method of building a list. Wrapping up These are far from being the only ways to make your jQuery code run better, but they are among the simplest ones to implement. Though each individual change may only make a few milliseconds of difference, it doesn’t take long for those milliseconds to add up. Studies have shown that the human eye can discern delays of as few as 100ms, so simply making a few changes sprinkled throughout your code can very easily have a noticeable effect on how well your website or app performs. Do you have other jQuery optimization tips to share? Leave them in the comments and help make us all better. 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