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<!DOCTYPE html>  <html lang="en"> <head> <meta charset="utf-8"> <title>CanJS - events</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'); ga('create', 'UA-2302003-11', 'auto'); ga('send', 'pageview'); </script> </head> <body> <input type="checkbox" id="nav-trigger" class="nav-trigger"/> <label for="nav-trigger">Menu</label> <div id="everything"> <div id="left" class="column"> <div class="top-left"> <div class="brand"> <div class="logo"> <a href="../index.html" alt="CanJS"></a> <div class="dropdown project-dropdown"> <a href="https://donejs.com/">DoneJS</a> <a href="http://stealjs.com/">StealJS</a> <a href="http://jquerypp.com/">jQuery ++</a> <a href="https://funcunit.com/">FuncUnit</a> <a href="http://documentjs.com/">DocumentJS</a> </div> </div> <div class="version"> <div class="version-number"> 3.0.0 </div> <div class="dropdown version-dropdown"> <a href="https://v2.canjs.com">2.3.27</a> </div> </div> </div> <div class="search-bar"> <p>   </p> </div> </div> <div class="bottom-left"> <div class="social-side-container"> <ul class="social-side"> <li> <a class="header-mobile github" href="https://github.com/canjs/canjs" target="_blank"><img class="social-icon-small" src="../docs/images/github.png">Github</a> </li> <li> <a class="header-mobile twitter" href="https://twitter.com/canjs" target="_blank"><img class="social-icon-small" src="../docs/images/twitter.png">Twitter</a> </li> </ul> <ul class="social-side"> <li> <a class="header-mobile" href="https://gitter.im/canjs/canjs" target="_blank">Chat</a> </li> <li> <a class="header-mobile" href="http://forums.donejs.com/c/canjs" target="_blank">Forum</a> </li> </ul> </div> <ul> <li class=" "> <a class="page" href="guides.html" title="Welcome to CanJS! 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For example:</p> <pre><code>Component.extend({ ViewModel: { limit: "number", offset: "number", next: function(){ this.offset = this.offset + this.limit; } }, events: { ".next click": function(){ this.viewModel.next() }, "{viewModel} limit": function(viewModel, ev, newValue){ console.log("limit is now", newValue); } } }) </code></pre> <p>A component's events object is used as the prototype of a <a href="can-control.html" title="Create organized, memory-leak free, rapidly performing, stateful controls with declarative event binding. Use Control to create UI controls like tabs, grids, and context menus, and organize them into higher-order business rules with can.route. It can serve as both a traditional view and a traditional controller.">can-control</a>. The control gets created on the component's element.</p> <p>The component's <a href="can-component.prototype.ViewModel.html" title="Provides or describes a constructor function that provides values and methods to the component's template. The constructor function is initialized with values specified by the component element's data bindings.">ViewModel</a> instance is available within event handlers as <code>this.viewModel</code>.</p> <p>The component element is available as <code>this.element</code>.</p> </div> <section class="body"> <h2>Use</h2> <p><a href="can-component.html" title="Create a custom element that can be used to manage widgets or application logic.">can-component</a>'s events object allows you to provide low-level <a href="can-control.html" title="Create organized, memory-leak free, rapidly performing, stateful controls with declarative event binding. Use Control to create UI controls like tabs, grids, and context menus, and organize them into higher-order business rules with can.route. It can serve as both a traditional view and a traditional controller.">can-control</a>-like abilities to a <code>Component</code> while still accessing the <code>Component</code>'s <a href="can-component.prototype.ViewModel.html" title="Provides or describes a constructor function that provides values and methods to the component's template. The constructor function is initialized with values specified by the component element's data bindings.">ViewModel</a>. The following example listens to clicks on elements with <code>className="next"</code> and calls <code>.next()</code> on the component's viewModel.</p> <div class='demo_wrapper' data-demo-src='demos/can-component/paginate_events_next.html'></div> <p>The events object can also listen to objects or properties on the component's <a href="can-component.prototype.ViewModel.html" title="Provides or describes a constructor function that provides values and methods to the component's template. The constructor function is initialized with values specified by the component element's data bindings.">ViewModel</a> instance. For instance, instead of using live-binding, we could listen to when offset changes and update the page manually:</p> <div class='demo_wrapper' data-demo-src='demos/can-component/paginate_events_next_update_page.html'></div> <p>Components have the ability to bind to special inserted and removed events that are called when a component's tag has been inserted into or removed from the page:</p> <pre><code> events: { "inserted": function(){ // called when the component's tag is inserted into the DOM }, "removed": function(){ // called when the component's tag is removed from the DOM } } </code></pre> <h2>High performance template rendering</h2> <p>While <a href="can-stache-bindings.html" title="Provides template event, one-way, and two-way bindings.">can-stache-bindings</a> conveniently allows you to call a <a href="can-component.prototype.ViewModel.html" title="Provides or describes a constructor function that provides values and methods to the component's template. The constructor function is initialized with values specified by the component element's data bindings.">ViewModel</a> method from a template like:</p> <pre><code><input ($change)="doSomething()"/> </code></pre> <p>This has the effect of binding an event handler directly to this element. Every element that has a <code>($click)</code> or similar attribute has an event handler bound to it. For a large grid or list, this could have a performance penalty.</p> <p>By contrast, events bound using <a href="can-component.html" title="Create a custom element that can be used to manage widgets or application logic.">can-component</a>'s events object use event delegation, which is useful for high performance template rendering. In a large grid or list, event delegation only binds a single event handler rather than one per row.</p> </section> <script type="text/javascript"> var docObject = {"src":{"path":"node_modules/can-component/docs/events.md"},"description":"\nListen to events on elements and observables.\n","types":[{"type":"Object","options":[],"description":"An object of event names and methods\nthat handle the event. For example:\n\n Component.extend({\n\t ViewModel: {\n\t\tlimit: \"number\",\n\t\toffset: \"number\",\n\t next: function(){\n\t this.offset = this.offset + this.limit;\n\t }\n\t },\n events: {\n \".next click\": function(){\n this.viewModel.next()\n },\n\t\t\"{viewModel} limit\": function(viewModel, ev, newValue){\n\t\t console.log(\"limit is now\", newValue);\n\t\t}\n }\n })\n\n\nA component's events object is used as the prototype of a [can-control]. The control gets created on the component's\nelement.\n\nThe component's [can-component.prototype.ViewModel] instance is available within event handlers as `this.viewModel`.\n\nThe component element is available as `this.element`.\n\n","template":[{"types":[{"type":"can-control.eventDescription"}]},{"types":[{"type":"can-control.eventHandler"}]}]}],"title":"events","name":"can-component.prototype.events","type":"property","parent":"can-component.prototype","comment":" ","pathToRoot":".."}; </script> </article> <footer><p>CanJS is part of <a href="http://donejs.com" target="_blank">DoneJS</a>. 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