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<!DOCTYPE html>  <html lang="en"> <head> <meta charset="utf-8"> <title>CanJS - Handle User Interaction</title> <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no"> <link rel="stylesheet" type="text/css" href="./static/bundles/bit-docs-site/static.css"> <link rel="shortcut icon" sizes="16x16 24x24 32x32 48x48 64x64" href="/docs/images/canjs_favicon.ico"> <link rel="apple-touch-icon" sizes="57x57" href="../docs/images/canjs_favicon_57x57.png"> <link rel="apple-touch-icon-precomposed" sizes="57x57" href="../docs/images/canjs_favicon_57x57.png"> <link rel="apple-touch-icon" sizes="72x72" href="../docs/images/canjs_favicon_72x72.png"> <link rel="apple-touch-icon" sizes="114x114" href="../docs/images/canjs_favicon_114x114.png"> <link rel="apple-touch-icon" sizes="120x120" href="../docs/images/canjs_favicon_128x128.png"> <link rel="apple-touch-icon" sizes="144x144" href="../docs/images/canjs_favicon_144x144.png"> <link rel="apple-touch-icon" sizes="152x152" href="../docs/images/canjs_favicon_152x152.png"> <meta content="yes" name="apple-mobile-web-app-capable"> <meta name="apple-mobile-web-app-status-bar-style" content="white-translucent"> <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','https://www.google-analytics.com/analytics.js','ga'); 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Event handlers specify how <a href="http://bitovi.com/blog/2010/10/a-crash-course-in-how-dom-events-work.html">JavaScript should respond to an event</a>.</p> <p>This recipe will introduce handling a click event using a <a href="http://canjs.com/docs/can.Control.html"><code>can.Control</code></a>. Using a list of people like previous recipes, clicking any individual person's name will remove that person from the list.</p> <p>Previous examples have used jQuery's event handlers:</p> <pre><code>$("#push").click(function(){ //handle the event }); </code></pre> <p>CanJS provides a few different ways to respond to events. As well as making application code simpler, using CanJS to handle events can help to automatically prevent <a href="http://bitovi.com/blog/2012/04/zombie-apocolypse.html">memory leaks</a>.</p> <p>To handle events, extend <code>can.Control</code>.</p> <pre><code>var PeopleList = can.Control.extend({ //behavior }); </code></pre> <p>You create a <code>can.Control</code> by <a href="http://canjs.com/docs/can.Control.html#sig_newcan_Control_element_options_">calling it as a constructor function</a>. The first argument is the element the control will be created on. The second argument is an object of options.</p> <pre><code>new PeopleList('#my-app', {people: people}); </code></pre> <p>A <code>can.Control</code> handles events with functions declared with two arguments: an element or list of elements (using a jQuery-style selector) and a specific event. Below, this is 'li click', meaning when any <code>li</code> elements that are <code>clicked</code> the function will be called to handle the click event.</p> <pre><code>var PeopleList = can.Control.extend({ init: function( element, options ){ this.people = new can.List(options.people); this.element.html( can.view('app-template', { //defines people in the template as the observable can.List people: this.people })); }, 'li click': function( li, event ){ //Handle the click event } }; </code></pre> <p>When the constructor function is called and the <code>can.Control</code> is instantiated:</p> <ol> <li>The <code>init</code> method is called</li> <li>An observable <code>can.List</code> is created from <code>people</code></li> <li>The list is rendered using <code>can.view</code> so when the list changes, so will the view</li> </ol> <pre><code>var people = [ {firstname: "John", lastname: "Doe"}, {firstname: "Emily", lastname: "Dickinson"}, {firstname: "William", lastname: "Adams"}, {firstname: "Stevie", lastname: "Nicks"}, {firstname: "Bob", lastname: "Barker"} ]; </code></pre> <p>When the event handler for a <code>click</code> runs, it needs a way to access the object associated with the <code>li</code> that was clicked. With the <a href="http://canjs.com/docs/can.stache.helpers.data.html"><code>data</code></a> helper, the element will retain a reference to the object it is associated with (in this case, a <code>person</code>).</p> <pre><code><ul> {{#each people}} <li {{data 'person'}}> {{lastname}}, {{firstname}} </li> {{/each}} </ul> </code></pre> <p>Finally, the event handler must be defined. In a <code>can.Control</code>, an event handler function <a href="http://canjs.com/docs/can.Control.html#section_Listeningtoevents">can be defined with a string containing a selector and an event</a>. In this case, these are <code>li</code> and <code>click</code>, respectively, since we want to handle click events on each list item.</p> <pre><code>var PeopleList = can.Control.extend({ init: function(){ ... }, 'li click': function( li, event ) { var people = this.people; var person = li.data('person'); var index = people.indexOf(person); people.splice(index, 1); } }); </code></pre> <p>When a user clicks a list item:</p> <ol> <li>The function bound to <code>li click</code> is called</li> <li>The object associated with that list item is accessed using the <code>data</code> helper</li> <li>That 'person's data is removed from the observable list of <code>people</code></li> <li>The template updates automatically</li> </ol> <p>As a reminder, though event handlers respond to actions on the page, they should <em>change application state or data</em> (e.g. make a change to a <code>can.Map</code>) rather than modifying the DOM directly (e.g. toggling a class). This will update the page automatically, keeping code manageable.</p> <p>This is <em>one</em> way to handle events. Others will be covered in the following recipes while building widgets.</p> <iframe width="100%" height="300" src="http://jsfiddle.net/donejs/F9kzt/embedded/result,html,js/" allowfullscreen="allowfullscreen" frameborder="0"> </iframe> </section> <script type="text/javascript"> var docObject = {"src":{"path":"docs/can-guides/recipes/handle-user-interaction.md"},"description":"\n","name":"HandleUserInteraction","title":"Handle User Interaction","type":"page","parent":"Recipes","order":4,"comment":" ","pathToRoot":".."}; </script> </article> <footer><p>CanJS is part of <a href="http://donejs.com" target="_blank">DoneJS</a>. 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