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The following recipes will introduce <code>can.Component</code>, which allows for straightforward widget construction by packaging template, state, and event handling code in one place.</p> <p>While similar <em>behavior</em> can be accomplished with <code>can.Control</code>, building a Component enables building reusable widgets using custom HTML tags.</p> <h2>Create a Component</h2> <p>The previous recipe that displays a list of people can instead be represented as a component.</p> <pre><code><people></people> </code></pre> <p>By specifying <code>people</code> as the tag, a component is created wherever <code><people></people></code> appears in a template.</p> <pre><code>can.Component.extend({ tag: 'people', </code></pre> <p>The <code>scope</code> object on a <code>Component</code> contains the component's state, data, and behavior. Here, it specifies how to <code>remove</code> a person from the list:</p> <pre><code> scope: { people: people, remove: function( person ) { var people = this.attr("people"); var index = people.indexOf(person); people.splice(index, 1); } } }); </code></pre> <p>The template for the component itself is passed via the <code>template</code> property. This can either be an external file or a string. Each <code>li</code> uses <code>can-click</code>, <a href="http://canjs.com/docs/can.view.bindings.can-EVENT.html">which declares an event binding.</a> Here, <code>remove</code> inside the component's scope will be called with the relevant <code>people</code> object as an argument.</p> <pre><code>scope: { template: '<ul>' + '{{#each people}}' + '<li can-click="remove">' + '{{lastname}}, {{firstname}}' + '</li>' + '{{/each}}' + '</ul>', ... </code></pre> <p>This behaves similarly to the <code>can.Control</code> from above. However, the <code><people></code> tag can be used without having any knowledge about the inner workings of the widget. Using declarative HTML tags, a component can be used without writing any javascript. The template, state, and behavior are all combined into one Component.</p> <iframe width="100%" height="300" src="http://jsfiddle.net/donejs/WBM9z/embedded/result,html,js/" allowfullscreen="allowfullscreen" frameborder="0"> </iframe> <h2>Build a Tabs Widget</h2> <p>A tabs widget could be instantiated with the following HTML:</p> <pre><code><tabs> <panel title="Fruit">Oranges, Apples, Pears</panel> <panel title="Vegetable">Carrot, Lettuce, Rutabega</panel> <panel title="Grains">Bread, Pasta, Rice</panel> </tabs> </code></pre> <p>A designer that understands HTML can put together a template for a <code>tabs</code> widget without understanding anything other than the syntax. This is one of the most useful features of components.</p> <h2>Tabs Widget Behavior</h2> <p>Before implementing the component itself, we’ll define an observable <em>view model</em>--the <code>scope</code> object of the UI element. This makes the code modular and easier to manage (and also allows for unit testing).</p> <p>In order to accurately represent a tabs widget, a <code>TabsViewModel</code> needs:</p> <ul> <li>An observable list of panels</li> <li>A state variable with the active panel</li> <li>Helper methods to add, remove, and activate panels</li> </ul> <p>Since TabsViewModel is a <code>can.Map</code>, the <code>panels</code> property is automatically converted to a <code>can.List</code>. The <code>active</code> property references the <code>panel</code> object that should currently be displayed.</p> <pre><code>var TabsViewModel = can.Map.extend({ panels: [], active: null, addPanel: function( panel ){ var panels = this.attr("panels"); panels.push(panel); panel.attr("visible", false); //activate panel if it is the first one if ( panels.attr("length") === 1 ){ this.activate( panel ); } }, removePanel: function( panel ){ var panels = this.attr("panels"); var index = panels.indexOf(panel); panels.splice(index, 1); //activate a new panel if panel being removed was the active panel if( this.attr("active") === panel ){ panels.attr("length") ? this.activate(panels[0]) : this.attr("active", null) } }, activate: function( panel ){ var active = this.attr("active") if( active !== panel ){ active && active.attr("visible", false); this.attr("active", panel.attr("visible", true)); } } }); </code></pre> <h3>Tabs Widget Component</h3> <p>Now that the view model is defined, making a component is simply a matter of defining the way the tabs widget is displayed.</p> <p>The template for a <code>tabs</code> component needs a list of panel titles that will <code>activate</code> that panel when clicked. By calling <code>activate</code> with a panel as the argument, the properties of the <code>panel</code> can be manipulated. By changing the <code>visible</code> property of a panel, a template can be used to display or hide the panel accordingly.</p> <p>For this component, our template should look something like this:</p> <pre><code><tabs> <panel title="Fruits">Apples, Oranges</panel> <panel title="Vegetables">Carrots, Celery</panel> </tabs> </code></pre> <p>A designer can create a <code>tabs</code> component with <code>panel</code> components inside it. The <code>template</code> object on the tabs component's scope needs to be able to render the content that is inside of the <code><tabs></code> tag. To do this, we simply use the <code><content></code> tag, which will render everything within the component's tags:</p> <pre><code>can.Component.extend({ tag: "tabs", scope: TabsViewModel, template: "<ul>\ {{#each panels}}\ <li can-click='activate'>{{title}}</li>\ {{/each}}\ </ul>\ <content />" }); </code></pre> <p>The <code>tabs</code> component contains panels, which are also defined as components. The tabs template contains the logic for whether the panel is visible (<code>visible</code> is controlled by the tabs component's <code>activate</code> method).</p> <p>Each panel's <code>scope</code> contains a title, which should be taken from the <code>title</code> attribute in the <code><panel></code> tag. If you want to set the string value of a Component's attribute as a <code>scope</code> variable, use <code>@'</code>.</p> <pre><code>can.Component.extend({ tag: "panel", template: "{{#if visible}}<content />{{/if}}", scope: { title: "@" }, ... </code></pre> <p>In addition to the <code>scope</code> property, a component has an <a href="http://canjs.com/docs/can.Component.prototype.events.html"><code>events</code> property</a>. This <code>events</code> property uses a <code>can.Control</code> instantiated inside the component to handle events.</p> <p>Since we defined behavior for adding panels on the parent <code>tabs</code> component, we should use this method whenever a <code>panel</code> is inserted into the page (and an <code>inserted</code> event is triggered). To add the panel to the <code>tabs</code> component's scope, we call the <code>addPanel</code> method by accessing the parent scope with <code>this.element.parent().scope()</code>:</p> <pre><code>... events: { inserted: function() { this.element.parent().scope().addPanel( this.scope ) }, removed: function() { this.element.parent().scope().addPanel( this.scope ) } } }); </code></pre> <p>With this component, any time a <code><tabs></code> element with <code><panel></code> elements is put in a page, a tabs widget will automatically be created. This allows application behavior and design to be compartmentalized from each other.</p> <iframe width="100%" height="300" src="http://jsfiddle.net/x6TJK/2/embedded/result,html,js/" allowfullscreen="allowfullscreen" frameborder="0"> </iframe> </section> <script type="text/javascript"> var docObject = {"src":{"path":"docs/can-guides/recipes/build-widgets.md"},"description":"\n","name":"BuildWidgets","title":"Build Widgets/UI Elements","type":"page","parent":"Recipes","order":5,"comment":" ","pathToRoot":".."}; </script> </article> <footer><p>CanJS is part of <a href="http://donejs.com" target="_blank">DoneJS</a>. 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