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Then, assigns every property on <code>props</code> to the new instance. If props are passed that are not defined already, those property definitions are created. If the instance should be sealed, it is sealed.</p> <pre><code class="language-js">var DefineMap = require("can-define/map/map"); var person = new DefineMap({ first: "Justin", last: "Meyer" }) </code></pre> <p>Custom <code>DefineMap</code> types, with special properties and behaviors, can be defined with <a href="map.extend.html" title="Define a custom map type.">extend</a>.</p> <div class="parameters"> <h3 class="parameters-title">Parameters</h3> <ol> <li><b>props</b> <code>{Object}</code>: <p>Properties and values to seed the map with.</p> </li> </ol> </div> <div class="returns"> <h3 class="returns-title">Returns</h3> <p> <code>{<a href="map.html" title="Create observable objects.">can-define/map/map</a>}</code>: <p>An instance of <code>DefineMap</code> with the properties from <em>props</em>.</p> </p> </div> </div> <section class="body"> <h2>Use</h2> <p><code>can-define/map/map</code> is used to create easily extensible observable types with well defined behavior.</p> <p>For example, a <code>Todo</code> type, with a <code>name</code> property, <code>completed</code> property, and a <code>toggle</code> method, might be defined like:</p> <pre><code class="language-js">var DefineMap = require("can-define/map/map"); var Todo = DefineMap.extend({ name: "string", completed: {type: "boolean", value: false}, toggle: function(){ this.completed = !this.completed; } }) </code></pre> <p>The <em>Object</em> passed to <code>.extend</code> defines the properties and methods that will be on <em>instances</em> of a <code>Todo</code>. There are a lot of ways to define properties. The <a href="../../can-define.types.propDefinition.html" title="Defines the type, initial value, and get, set, and serialize behavior for an observable property. These behaviors can be specified with as an Object, String, Constructor function, Array, a getter expression, or setter expression.">PropDefinition</a> type lists them all. Here, we define:</p> <ul> <li><code>name</code> as a property that will be type coerced into a <code>String</code>.</li> <li><code>completed</code> as a property that will be type coerced into a <code>Boolean</code> with an initial value of <code>false</code>.</li> </ul> <p>This also defines a <code>toggle</code> method that will be available on <em>instances</em> of <code>Todo</code>.</p> <p><code>Todo</code> is a constructor function. This means <em>instances</em> of <code>Todo</code> can be be created by calling <code>new Todo()</code> as follows:</p> <pre><code class="language-js">var myTodo = new Todo(); myTodo.name = "Do the dishes"; myTodo.completed //-> false myTodo.toggle(); myTodo.completed //-> true </code></pre> <p>You can also pass initial properties and their values when initializing a <code>DefineMap</code>:</p> <pre><code class="language-js">var anotherTodo = new Todo({name: "Mow lawn", completed: true}); myTodo.name = "Mow lawn"; myTodo.completed //-> true </code></pre> <h2>Declarative properties</h2> <p>Arguably <code>can-define</code>'s most important ability is its support of declarative properties that functionally derive their value from other property values. This is done by defining <a href="../../can-define.types.get.html" title="Specify what happens when a certain property is read on a map. get functions work like a can-compute and automatically update themselves when a dependent observable value is changed.">getter</a> properties like <code>fullName</code> as follows:</p> <pre><code class="language-js">var Person = DefineMap.extend({ first: "string", last: "string", fullName: { get : function(){ return this.first + " " + this.last; } } }); </code></pre> <p><code>fullName</code> can also be defined with the ES5 shorthand getter syntax:</p> <pre><code class="language-js">var Person = DefineMap.extend({ first: "string", last: "string", get fullName(){ return this.first + " " + this.last; } }); </code></pre> <p>Now, when a <code>person</code> is created, there is a <code>fullName</code> property available like:</p> <pre><code class="language-js">var me = new Person({first: "Harry", last: "Potter"}); me.fullName //-> "Harry Potter" </code></pre> <p>This property can be bound to like any other property:</p> <pre><code class="language-js">me.on("fullName", function(ev, newValue, oldValue){ newValue //-> Harry Henderson oldValue //-> Harry Potter }); me.last = "Henderson"; </code></pre> <p><code>getter</code> properties use <a href="../../can-compute.html" title="Create an observable value.">can-compute</a> internally. This means that when bound, the value of the <code>getter</code> is cached and only updates when one of its source observables change. For example:</p> <pre><code class="language-js">var Person = DefineMap.extend({ first: "string", last: "string", get fullName(){ console.log("calculating fullName"); return this.first + " " + this.last; } }); var hero = new Person({first: "Wonder", last: "Woman"}); // console.logs "calculating fullName" hero.fullName //-> Wonder Woman // console.logs "calculating fullName" hero.fullName //-> Wonder Woman // console.logs "calculating fullName" hero.on("fullName", function(){}); hero.fullName //-> "Wonder Woman" // console.logs "calculating fullName" hero.first = "Bionic" // console.logs "calculating fullName" hero.last = "Man" hero.fullName //-> "Bionic Man" </code></pre> <p>If you want to prevent repeat updates, use <a href="../../can-event/batch/batch.html" title="Adds task batching abilities to event dispatching.">can-event/batch/batch</a>:</p> <pre><code class="language-js">hero.fullName //-> "Bionic Man" var canBatch = require("can-event/batch/batch"); canBatch.start(); hero.first = "Silk"; hero.last = "Spectre"; // console.logs "calculating fullName" canBatch.stop(); </code></pre> <h3>Asynchronous getters</h3> <p><code>getters</code> can also be asynchronous. These are very useful when you have a type that requires data from the server. This is very common in <a href="../../can-component.html" title="Create a custom element that can be used to manage widgets or application logic.">can-component</a> view-models. For example, a <code>view-model</code> might take a <code>todoId</code> value, and want to make a <code>todo</code> property available:</p> <pre><code class="language-js">var ajax = require("can-util/dom/ajax/ajax"); var TodoViewModel = DefineMap.extend({ todoId: "number", todo: function(lastSetValue, resolve){ ajax({url: "/todos/"+this.todoId}).then(resolve) } }); </code></pre> <p>Asynchronous getters only are passed a <code>resolve</code> argument when bound. Typically in an application, your template will automatically bind on the <code>todo</code> property. But to use it in a test might look like:</p> <pre><code class="language-js">var fixture = require("can-fixture"); fixture("GET /todos/5", function(){ return {id: 5, name: "take out trash"} }); var todoVM = new TodoViewModel({id: 5}); todoVM.on("todo", function(ev, newVal){ assert.equal(newVal.name, "take out trash"); }); </code></pre> <h3>Getter limitations</h3> <p>There's some functionality that a getter or an async getter can not describe declaratively. For these situations, you can use <a href="../../can-define.types.set.html" title="Specify what happens when a property value is set.">set</a> or even better, use the <a href="../../can-define-stream.html" title="Define property values using streams. can-stream is used internally to provide the stream functionality.">can-define-stream</a> plugin.</p> <p>For example, consider a <strong>state</strong> and <strong>city</strong> locator where you pick a United States <strong>state</strong> like <em>Illinois</em> and then a <strong>city</strong> like <em>Chicago</em>. In this example, we want to clear the choice of <strong>city</strong> whenever the <strong>state</strong> changes.</p> <p>This can be implemented with <a href="../../can-define.types.set.html" title="Specify what happens when a property value is set.">set</a> like:</p> <pre><code class="language-js">Locator = DefineMap.extend({ state: { type: "string", set: function(){ this.city = null; } }, city: "string" }); var locator = new Locator({ state: "IL", city: "Chicago" }); locator.state = "CA"; locator.city //-> null; </code></pre> <p>This isn't declarative anymore because changing state imperatively changes the value of <code>city</code>. The <a href="../../can-define-stream.html" title="Define property values using streams. can-stream is used internally to provide the stream functionality.">can-define-stream</a> plugin can make this functionality entirely declarative.</p> <pre><code class="language-js">var Locator = DefineMap.extend({ state: "string", city: { type: "string", stream: function(setStream) { return this.stream(".state").map(function(){ return null; }).merge(setStream); } } }); var locator = new Locator({ state: "IL", city: "Chicago" }); locator.on("city", function(){}); locator.state = "CA"; locator.city //-> null; </code></pre> <p>Notice, in the <code>can-define-stream</code> example, <code>city</code> must be bound for it to work.</p> <h2>Sealed instances and strict mode</h2> <p>By default, <code>DefineMap</code> instances are <a href="map.seal.html" title="Defines if instances of the map should be sealed in development.">sealed</a>. This means that setting properties that are not defined when the constructor is defined will throw an error in files that are in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode">strict mode</a>. For example:</p> <pre><code class="language-js">"use strict"; var DefineMap = require("can-define/map/map"); var MyType = DefineMap.extend({ myProp: "string" }); var myType = new MyType(); myType.myProp = "value"; // no error thrown myType.otherProp = "value" // throws Error! </code></pre> <p>Read the <a href="map.seal.html" title="Defines if instances of the map should be sealed in development.">seal</a> documentation for more information on this behavior.</p> </section> <script type="text/javascript"> var docObject = {"src":{"path":"node_modules/can-define/map/docs/define-map.md"},"description":"Create observable objects. \n","type":"module","title":"","types":[{"type":"function","returns":{"types":[{"type":"undefined"}]},"params":[]}],"name":"can-define/map/map","parent":"can-core","alias":"can.DefineMap","inherits":"can.Construct","signatures":[{"code":"new DefineMap([props])","description":"\n\nThe `can-define/map/map` module exports the `DefineMap` constructor function. \n\nCalling `new DefineMap(props)` creates a new instance of DefineMap or an [can-define/map/map.extend extended] DefineMap. Then, assigns every property on `props` to the new instance. If props are passed that are not defined already, those property definitions are created. If the instance should be sealed, it is sealed.\n\n```js\nvar DefineMap = require(\"can-define/map/map\");\n\nvar person = new DefineMap({\n first: \"Justin\",\n last: \"Meyer\"\n})\n```\n\n Custom `DefineMap` types, with special properties and behaviors, can be defined with [can-define/map/map.extend].\n","params":[{"types":[{"type":"Object","options":[]}],"optional":true,"name":"props","description":"Properties and values to seed the map with."}],"returns":{"types":[{"type":"can-define/map/map"}],"description":"An instance of `DefineMap` with the properties from _props_.\n"}}],"_curParam":{"types":[{"type":"Object","options":[]}],"optional":true,"name":"props","description":"Properties and values to seed the map with."},"_curReturn":{"types":[{"type":"can-define/map/map"}],"description":"An instance of `DefineMap` with the properties from _props_.\n"},"comment":" ","pathToRoot":"../../.."}; </script> </article> <footer><p>CanJS is part of <a href="http://donejs.com" target="_blank">DoneJS</a>. 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