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data-show-screen-name="false">Follow @canjs</a><script async src="//platform.twitter.com/widgets.js" charset="utf-8"></script> </li> </ul> </div> <div class="breadcrumb"> <li><a href="../index.html">CanJS</a></li> / <li><a href="can-legacy.html">Legacy</a></li> / <li><a href="can-list.html">can-list</a></li> / <li><a href="can-list.prototype.attr.html">attr</a></li> <li class="breadcrumb-dropdown">/ <a> On this page</a> <ul class="on-this-page"></ul> </li> <div class="nav-toggle" title="Back to top"></div> </div> </div> <div class="bottom-right"> <article> <section class="title"> <div class="page-type"> <h1>attr</h1> <div>function</div> </div> <section class="description"> <p>Get or set elements in a List.</p> </section> </section> <section class="on-this-page-table"> </section> <section class="title-footer"> <ul class="title-links">  <li><a href="//github.com/canjs/can-list/tree/v3.0.0/docs/prototype.attr.md">source</a></li>   </ul> </section> <div class="signature"> <h2 class="signature-title"> <code>list.attr()</code> </h2> <p>Gets an array of all the elements in this <code>List</code>.</p> <div class="returns"> <h3 class="returns-title">Returns</h3> <p> <code>{Array}</code>: <p>An array with all the elements in this List.</p> </p> </div> </div> <div class="signature"> <h2 class="signature-title"> <code>list.attr(index)</code> </h2> <p>Reads an element from this <code>List</code>.</p> <div class="parameters"> <h3 class="parameters-title">Parameters</h3> <ol> <li><b>index</b> <code>{Number}</code>: <p>The element to read.</p> </li> </ol> </div> <div class="returns"> <h3 class="returns-title">Returns</h3> <p> <code>{*}</code>: <p>The value at <em>index</em>.</p> </p> </div> </div> <div class="signature"> <h2 class="signature-title"> <code>list.attr(index, value)</code> </h2> <p>Assigns <em>value</em> to the index <em>index</em> on this <code>List</code>, expanding the list if necessary.</p> <div class="parameters"> <h3 class="parameters-title">Parameters</h3> <ol> <li><b>index</b> <code>{Number}</code>: <p>The element to set.</p> </li> <li><b>value</b> <code>{*}</code>: <p>The value to assign at <em>index</em>.</p> </li> </ol> </div> <div class="returns"> <h3 class="returns-title">Returns</h3> <p> <code>{<a href="can.List.html" title="undefined">can.List</a>}</code>: <p>This list, for chaining.</p> </p> </div> </div> <div class="signature"> <h2 class="signature-title"> <code>list.attr(elements[, replaceCompletely])</code> </h2> <p>Merges the members of <em>elements</em> into this List, replacing each from the beginning in order. If <em>elements</em> is longer than the current List, the current List will be expanded. If <em>elements</em> is shorter than the current List, the extra existing members are not affected (unless <em>replaceCompletely</em> is <code>true</code>). To remove elements without replacing them, use <code><a href="can-map.prototype.removeAttr.html" title="Remove a property from a Map.">removeAttr</a></code>.</p> <div class="parameters"> <h3 class="parameters-title">Parameters</h3> <ol> <li><b>elements</b> <code>{Array}</code>: <p>An array of elements to merge in.</p> </li> <li><b>replaceCompletely</b> <code>{bool}</code>: <p>whether to completely replace the elements of List</p> <p>If <em>replaceCompletely</em> is <code>true</code> and <em>elements</em> is shorter than the List, the existing extra members of the List will be removed.</p> </li> </ol> </div> <div class="returns"> <h3 class="returns-title">Returns</h3> <p> <code>{<a href="can.List.html" title="undefined">can.List</a>}</code>: <p>This list, for chaining.</p> </p> </div> </div> <section class="body"> <h2>Use</h2> <p><code>attr</code> gets or sets elements on the <code>List</code> it's called on. Here's a tour through how all of its forms work:</p> <pre><code> var people = new List(['Alex', 'Bill']); // set an element: people.attr(0, 'Adam'); // get an element: people.attr(0); // 'Adam' people[0]; // 'Adam' // get all elements: people.attr(); // ['Adam', 'Bill'] // extend the array: people.attr(4, 'Charlie'); people.attr(); // ['Adam', 'Bill', undefined, undefined, 'Charlie'] // merge the elements: people.attr(['Alice', 'Bob', 'Eve']); people.attr(); // ['Alice', 'Bob', 'Eve', undefined, 'Charlie'] </code></pre> <h2>Deep properties</h2> <p><code>attr</code> can also set and read deep properties. All you have to do is specify the property name as you normally would if you weren't using <code>attr</code>.</p> <pre><code>var people = new List([{name: 'Alex'}, {name: 'Bob'}]); // set a property: people.attr('0.name', 'Alice'); // get a property: people.attr('0.name'); // 'Alice' people[0].attr('name'); // 'Alice' // get all properties: people.attr(); // [{name: 'Alice'}, {name: 'Bob'}] </code></pre> <p>The discussion of deep properties under <code><a href="can-map.prototype.attr.html" title="Get or set properties on a Map.">attr</a></code> may also be enlightening.</p> <h2>Events</h2> <p><code>List</code>s emit five types of events in response to changes. They are:</p> <ul> <li>the <em>change</em> event fires on every change to a List.</li> <li>the <em>set</em> event is fired when an element is set.</li> <li>the <em>add</em> event is fired when an element is added to the List.</li> <li>the <em>remove</em> event is fired when an element is removed from the List.</li> <li>the <em>length</em> event is fired when the length of the List changes.</li> </ul> <h3>The <em>change</em> event</h3> <p>The first event that is fired is the <em>change</em> event. The <em>change</em> event is useful if you want to react to all changes on an List.</p> <pre><code>var list = new List([]); list.bind('change', function(ev, index, how, newVal, oldVal) { console.log('Something changed.'); }); </code></pre> <p>The parameters of the event handler for the <em>change</em> event are:</p> <ul> <li><em>ev</em> The event object.</li> <li><em>index</em> Where the change took place.</li> <li><em>how</em> Whether elements were added, removed, or set. Possible values are <code>'add'</code>, <code>'remove'</code>, or <code>'set'</code>.</li> <li><em>newVal</em> The elements affected after the change <em>newVal</em> will be a single value when an index is set, an Array when elements were added, and <code>undefined</code> if elements were removed.</li> <li><em>oldVal</em> The elements affected before the change. <em>newVal</em> will be a single value when an index is set, an Array when elements were removed, and <code>undefined</code> if elements were added.</li> </ul> <p>Here is a concrete tour through the <em>change</em> event handler's arguments:</p> <pre><code>var list = new List(); list.bind('change', function(ev, index, how, newVal, oldVal) { console.log(ev + ', ' + index + ', ' + how + ', ' + newVal + ', ' + oldVal); }); list.attr(['Alexis', 'Bill']); // [object Object], 0, add, ['Alexis', 'Bill'], undefined list.attr(2, 'Eve'); // [object Object], 2, add, Eve, undefined list.attr(0, 'Adam'); // [object Object], 0, set, Adam, Alexis list.attr(['Alice', 'Bob']); // [object Object], 0, set, Alice, Adam // [object Object], 1, set, Bob, Bill list.removeAttr(1); // [object Object], 1, remove, undefined, Bob </code></pre> <h3>The <em>set</em> event</h3> <p><em>set</em> events are fired when an element at an index that already exists in the List is modified. Actions can cause <em>set</em> events to fire never also cause <em>length</em> events to fire (although some functions, such as <code><a href="can-list.prototype.splice.html" title="Insert and remove elements from a List.">splice</a></code> may cause unrelated sets of events to fire after being batched).</p> <p>The parameters of the event handler for the <em>set</em> event are:</p> <ul> <li><em>ev</em> The event object.</li> <li><em>newVal</em> The new value of the element.</li> <li><em>index</em> where the set took place.</li> </ul> <p>Here is a concrete tour through the <em>set</em> event handler's arguments:</p> <pre><code>var list = new List(); list.bind('set', function(ev, newVal, index) { console.log(newVal + ', ' + index); }); list.attr(['Alexis', 'Bill']); list.attr(2, 'Eve'); list.attr(0, 'Adam'); // Adam, 0 list.attr(['Alice', 'Bob']); // Alice, 0 // Bob, 1 list.removeAttr(1); </code></pre> <h3>The <em>add</em> event</h3> <p><em>add</em> events are fired when elements are added or inserted into the List.</p> <p>The parameters of the event handler for the <em>add</em> event are:</p> <ul> <li><em>ev</em> The event object.</li> <li><em>newElements</em> The new elements. If more than one element is added, <em>newElements</em> will be an array. Otherwise, it is simply the new element itself.</li> <li><em>index</em> Where the add or insert took place.</li> </ul> <p>Here is a concrete tour through the <em>add</em> event handler's arguments:</p> <pre><code>var list = new List(); list.bind('add', function(ev, newElements, index) { console.log(newElements + ', ' + index); }); list.attr(['Alexis', 'Bill']); // ['Alexis', 'Bill'], 0 list.attr(2, 'Eve'); // Eve, 2 list.attr(0, 'Adam'); list.attr(['Alice', 'Bob']); list.removeAttr(1); </code></pre> <h3>The <em>remove</em> event</h3> <p><em>remove</em> events are fired when elements are removed from the list.</p> <p>The parameters of the event handler for the <em>remove</em> event are:</p> <ul> <li><em>ev</em> The event object.</li> <li><em>removedElements</em> The removed elements. If more than one element was removed, <em>removedElements</em> will be an array. Otherwise, it is simply the element itself.</li> <li><em>index</em> Where the removal took place.</li> </ul> <p>Here is a concrete tour through the <em>remove</em> event handler's arguments:</p> <pre><code>var list = new List(); list.bind('remove', function(ev, removedElements, index) { console.log(removedElements + ', ' + index); }); list.attr(['Alexis', 'Bill']); list.attr(2, 'Eve'); list.attr(0, 'Adam'); list.attr(['Alice', 'Bob']); list.removeAttr(1); // Bob, 1 </code></pre> <h3>The <em>length</em> event</h3> <p><em>length</em> events are fired whenever the list changes.</p> <p>The parameters of the event handler for the <em>length</em> event are:</p> <ul> <li><em>ev</em> The event object.</li> <li><em>length</em> The current length of the list. If events were batched when the <em>length</em> event was triggered, <em>length</em> will have the length of the list when <code>stopBatch</code> was called. Because of this, you may receive multiple <em>length</em> events with the same <em>length</em> parameter.</li> </ul> <p>Here is a concrete tour through the <em>length</em> event handler's arguments:</p> <pre><code>var list = new List(); list.bind('length', function(ev, length) { console.log(length); }); list.attr(['Alexis', 'Bill']); // 2 list.attr(2, 'Eve'); // 3 list.attr(0, 'Adam'); list.attr(['Alice', 'Bob']); list.removeAttr(1); // 2 </code></pre> </section> <script type="text/javascript"> var docObject = {"src":{"path":"node_modules/can-list/docs/prototype.attr.md"},"description":"Get or set elements in a List. \n","title":"attr","name":"can-list.prototype.attr","type":"function","parent":"can-list.prototype","signatures":[{"code":"list.attr()","description":"\n\nGets an array of all the elements in this `List`.\n","params":[],"returns":{"types":[{"type":"Array","options":[]}],"description":"An array with all the elements in this List.\n"}},{"code":"list.attr(index)","description":"\n\nReads an element from this `List`.\n","params":[{"types":[{"type":"Number"}],"name":"index","description":"The element to read."}],"returns":{"types":[{"type":"*"}],"description":"The value at _index_.\n"}},{"code":"list.attr(index, value)","description":"\n\nAssigns _value_ to the index _index_ on this `List`, expanding the list if necessary.\n","params":[{"types":[{"type":"Number"}],"name":"index","description":"The element to set."},{"types":[{"type":"*"}],"name":"value","description":"The value to assign at _index_."}],"returns":{"types":[{"type":"can.List"}],"description":"This list, for chaining.\n"}},{"code":"list.attr(elements[, replaceCompletely])","description":"\n\nMerges the members of _elements_ into this List, replacing each from the beginning in order. 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