can

<!DOCTYPE html>  <html lang="en"> <head> <meta charset="utf-8"> <title>CanJS - attribute definition</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! These guides are here to help you develop and improve your relationship with CanJS. After all, picking a JavaScript framework is a commitment. We want CanJS to be the framework you marry. This page helps you know how advance through the different stages of this relationship:"> Guides </a> </li> <li class=" "> <a class="page" href="can-core.html" title="The best, most hardened and generally useful libraries in CanJS."> Core </a> </li> <li class=" "> <a class="page" href="can-ecosystem.html" title="Useful libraries that extend or add important features to the core collection."> Ecosystem </a> </li> <li class=" "> <a class="page" href="can-infrastructure.html" title="Utility libraries that power the core and ecosystem collection."> Infrastructure </a> </li> <li class=" parent expanded"> <a class="page" href="can-legacy.html" title="Former libraries that we still accept patches for, but are not under active development."> Legacy </a> <ul> <li class=" "> <a class="module" href="can-ejs.html" title="EJS provides live ERB-style client-side templates."> can-ejs </a> </li> <li class=" "> <a class="module" href="can-list.html" title=""> can-list </a> </li> <li class=" "> <a class="module" href="can-map.html" title="Create observable objects."> can-map </a> </li> <li class=" "> <a class="module" href="can-map-backup.html" title=""> can-map-backup </a> </li> <li class=" parent expanded"> <a class="module" href="can-map-define.html" title="Defines the type, initial value, get, set, remove, and serialize behavior for attributes of a Map."> can-map-define </a> <ul> <li class=" "> <a class="function" href="can-map-define.TypeConstructor.html" title="Provides a constructor function to be used to convert any value passed into attr into an appropriate value"> Type </a> </li> <li class=" "> <a class="function" href="can-map-define.ValueConstructor.html" title="Provides a constructor function to be used to provide a default value for a certain property of a Map. This constructor will be invoked with new each time a new instance of the map is created."> Value </a> </li> <li class=" "> <a class="function" href="can-map-define._type.html" title="Converts a value passed to attr into an appropriate value."> type </a> </li> <li class="current parent expanded"> <a class="typedef" href="can-map-define.attrDefinition.html" title="Defines the type, initial value, and get, set, and remove behavior for an attribute of a Map."> attribute definition </a> </li> <li class=" "> <a class="function" href="can-map-define.get.html" title="Specify what happens when a certain property is read on a map. get functions work like a compute and automatically update themselves when a dependent observable value is changed."> get </a> </li> <li class=" "> <a class="function" href="can-map-define.remove.html" title="Called when an attribute is removed."> remove </a> </li> <li class=" "> <a class="function" href="can-map-define.serialize.html" title="Called when an attribute is removed."> serialize </a> </li> <li class=" "> <a class="function" href="can-map-define.set.html" title="Specify what happens when a value is set on a map attribute."> set </a> </li> <li class=" "> <a class="function" href="can-map-define.value.html" title="Returns the default value for instances of this Map. This is called before init."> value </a> </li> </ul> </li> <li class=" "> <a class="module" href="can-view-href.html" title="Sets an element's href attribute so that it's url will set the specified attribute values on can-route."> can-view-href </a> </li> </ul> </li> </ul> </div> </div> <div id="right" class="column"> <div class="top-right"> <div class="top-right-top"> <ul class="top-right-bitovi"> <li class="dropdown"> <a href="http://bitovi.com" class="bitovi icon-bits">Bitovi</a> <ul class="dropdown-menu"> <li><a href="http://bitovi.com">Bitovi.com</a></li> <li><a href="http://bitovi.com/blog/">Blog</a></li> <li><a href="http://bitovi.com/consulting/">Consulting</a></li> <li><a href="http://bitovi.com/training/">Training</a></li> <li><a href="http://bitovi.com/open-source/">Open Source</a></li> </ul> </li> </ul> <div class="brand"> <div class="logo"> <a href="../index.html" alt="CanJS"></a> </div> </div> <ul class="top-right-links"> <li> <a href="https://gitter.im/canjs/canjs">Chat</a> </li> <li> <a href="http://forums.donejs.com/c/canjs">Forum</a> </li> <li> <a class="github-button nav-social" href="https://github.com/canjs/canjs" data-count-href="/canjs/canjs/stargazers" data-count-api="/repos/canjs/canjs#stargazers_count">Star</a> </li> <li> <a href="https://twitter.com/canjs" class="twitter-follow-button nav-social" data-show-count="true" 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-map-define.html">can-map-define</a></li> / <li><a href="can-map-define.attrDefinition.html">attribute definition</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>attribute definition</h1> <div>typedef</div> </div> <section class="description"> <p>Defines the type, initial value, and get, set, and remove behavior for an attribute of a <a href="can-map.html" title="Create observable objects.">Map</a>.</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-map-define/tree/v3.0.0/docs/attrDefinition.md">source</a></li>   </ul> </section> <div class="signature"> <h2 class="signature-title"> <code>Object</code> </h2> <div class="options"> <h3 class="options-title">Options</h3> <ul> <li> <b>value</b> <code>{<a href="can-map-define.value.html" title="Returns the default value for instances of this Map. This is called before init.">value</a>()|*}</code>: <p>Specifies the initial value of the attribute or a function that returns the initial value. For example, a default value of <code>0</code> can be specified like:</p> <pre><code>define: { prop: { value: 0 } } </code></pre> <p><code>Object</code> types should not be specified directly on <code>value</code> because that same object will be shared on every instance of the Map. Instead, a <a href="can-map-define.value.html" title="Returns the default value for instances of this Map. This is called before init.">value function</a> that returns a fresh copy can be provided:</p> <pre><code>define: { prop: { value: function(){ return {foo: "bar"} } } } </code></pre> </li> <li> <b>Value</b> <code>{function}</code>: <p>Specifies a function that will be called with <code>new</code> whose result is set as the initial value of the attribute. For example, if the default value should be a <a href="can-list.html" title="">List</a>:</p> <pre><code>define: { prop: { Value: Map.List } } </code></pre> </li> <li> <b>type</b> <code>{<a href="can-map-define._type.html" title="Converts a value passed to attr into an appropriate value.">type</a>(newValue, attrName)|String}</code>: <p>Specifies the type of the attribute. The type can be specified as either a <a href="can-map-define._type.html" title="Converts a value passed to attr into an appropriate value.">type function</a> that returns the type coerced value or one of the following strings:</p> <ul> <li><code>"string"</code> - Converts the value to a string.</li> <li><code>"date"</code> - Converts the value to a date or `null if the date can not be converted.</li> <li><code>"number"</code> - Passes the value through <code>parseFloat</code>.</li> <li><code>"boolean"</code> - Converts falsey, <code>"false"</code> or <code>"0"</code> to <code>false</code> and everything else to true.</li> <li><code>"*"</code> - Prevents the default type coersion of converting Objects to <a href="can-map.html" title="Create observable objects.">Map</a>s and Arrays to <a href="can-list.html" title="">List</a>s.</li> </ul> <p>The following example converts the <code>count</code> property to a number and the <code>items</code> property to an array:</p> <pre><code> define: { count: {type: "number"}, items: { type: function(newValue){ if(typeof newValue === "string") { return newValue.split(",") } else if( can.isArray(newValue) ) { return newValue; } } } } </code></pre> </li> <li> <b>Type</b> <code>{<a href="can-map-define.TypeConstructor.html" title="Provides a constructor function to be used to convert any value passed into attr into an appropriate value">Type</a>()}</code>: <p>A constructor function that takes the value passed to <a href="can-map.prototype.attr.html" title="Get or set properties on a Map.">attr</a> as the first argument and called with new. For example, if you want whatever gets passed to go through <code>new Array(newValue)</code> you can do that like:</p> <pre><code>define: { items: { Type: Array } } </code></pre> <p>If the value passed to <a href="can-map.prototype.attr.html" title="Get or set properties on a Map.">attr</a> is already an Array, it will be left as is.</p> </li> <li> <b>set</b> <code>{<a href="can-map-define.set.html" title="Specify what happens when a value is set on a map attribute.">set</a>(newVal, setValue)}</code>: <p>A set function that specifies what should happen when an attribute is set on a <a href="can-map.html" title="Create observable objects.">can-map</a>. <code>set</code> is called with the result of <code>type</code> or <code>Type</code>. The following defines a <code>page</code> setter that updates the map's offset:</p> <pre><code>define: { page: { set: function(newVal){ this.attr('offset', (parseInt(newVal) - 1) * this.attr('limit')); } } } </code></pre> </li> <li> <b>get</b> <code>{<a href="can-map-define.get.html" title="Specify what happens when a certain property is read on a map. get functions work like a compute and automatically update themselves when a dependent observable value is changed.">get</a>(lastSetValue)}</code>: <p>A function that specifies how the value is retrieved. The get function is converted to an <a href="can-compute.async.html" title="Create a compute that can set its value after the computed function has been called.">async compute</a>. It should derive its value from other values on the map. The following defines a <code>page</code> getter that reads from a map's offset and limit:</p> <pre><code>define: { page: { get: function (newVal) { return Math.floor(this.attr('offset') / this.attr('limit')) + 1; } } } </code></pre> <p>A <code>get</code> definition makes the property <strong>computed</strong> which means it will not be serialized by default.</p> </li> <li> <b>remove</b> <code>{<a href="can-map-define.remove.html" title="Called when an attribute is removed.">remove</a>()}</code>: <p>A function that specifies what should happen when an attribute is removed with <a href="can-map.prototype.removeAttr.html" title="Remove a property from a Map.">removeAttr</a>. The following removes a <code>modelId</code> when <code>makeId</code> is removed:</p> <pre><code>define: { makeId: { remove: function(){ this.removeAttr("modelId"); } } } </code></pre> </li> <li> <b>serialize</b> <code>{<a href="can-map-define.serialize.html" title="Called when an attribute is removed.">serialize</a>(value, attr)|Boolean}</code>: <p>Specifies the behavior of the property when <a href="can-map.prototype.serialize.html" title="Serialize this object to something that can be passed to JSON.stringify.">serialize</a> is called.</p> <p>By default, serialize does not include computed values. Properties with a <code>get</code> definition are computed and therefore are not added to the result. Non-computed properties values are serialized if possible and added to the result.</p> <pre><code>Paginate = Map.extend({ define: { pageNum: { get: function(){ return this.offset() / 20 } } } }); p = new Paginate({offset: 40}); p.serialize() //-> {offset: 40} </code></pre> <p>If <code>true</code> is specified, computed properties will be serialized and added to the result.</p> <pre><code>Paginate = Map.extend({ define: { pageNum: { get: function(){ return this.offset() / 20 }, serialize: true } } }); p = new Paginate({offset: 40}); p.serialize() //-> {offset: 40, pageNum: 2} </code></pre> <p>If <code>false</code> is specified, non-computed properties will not be added to the result.</p> <pre><code>Paginate = Map.extend({ define: { offset: { serialize: false } } }); p = new Paginate({offset: 40}); p.serialize() //-> {} </code></pre> <p>If a <a href="can-map-define.serialize.html" title="Called when an attribute is removed.">serialize function</a> is specified, the result of the function is added to the result.</p> <pre><code>Paginate = Map.extend({ define: { offset: { serialize: function(offset){ return (offset / 20)+1 } } } }); p = new Paginate({offset: 40}); p.serialize() //-> {offset: 3} </code></pre> </li> </ul> </div> </div> <section class="body"> </section> <script type="text/javascript"> var docObject = {"src":{"path":"node_modules/can-map-define/docs/attrDefinition.md"},"description":"\nDefines the type, initial value, and get, set, and remove behavior for an attribute of a [can-map Map].\n","type":"typedef","title":"attribute definition","types":[{"type":"Object","options":[{"name":"value","description":"Specifies the initial value of the attribute or\na function that returns the initial value. For example, a default value of `0` can be \nspecified like:\n\n define: {\n prop: {\n value: 0\n }\n }\n\n`Object` types should not be specified directly on `value` because that same object will\nbe shared on every instance of the Map. Instead, a [can-map-define.value value function] that \nreturns a fresh copy can be provided:\n\n define: {\n prop: {\n value: function(){\n return {foo: \"bar\"}\n }\n }\n }\n","types":[{"type":"can-map-define.value"},{"type":"*"}]},{"name":"Value","description":"Specifies a function that will be called with `new` whose result is\nset as the initial value of the attribute. For example, if the default value should be a [can-list List]:\n\n define: {\n prop: {\n Value: Map.List\n }\n }\n","types":[{"type":"function","returns":{"types":[{"type":"undefined"}]},"params":[]}]},{"name":"type","description":"Specifies the type of the \nattribute. The type can be specified as either a [can-map-define._type type function] \nthat returns the type coerced value or one of the following strings:\n\n - `\"string\"` - Converts the value to a string.\n - `\"date\"` - Converts the value to a date or `null if the date can not be converted.\n - `\"number\"` - Passes the value through `parseFloat`.\n - `\"boolean\"` - Converts falsey, `\"false\"` or `\"0\"` to `false` and everything else to true.\n - `\"*\"` - Prevents the default type coersion of converting Objects to [can-map Map]s and Arrays to [can-list List]s.\n\nThe following example converts the `count` property to a number and the `items` property to an array:\n\n define: {\n count: {type: \"number\"},\n items: {\n type: function(newValue){\n if(typeof newValue === \"string\") {\n return newValue.split(\",\")\n } else if( can.isArray(newValue) ) {\n return newValue;\n }\n }\n }\n }\n","types":[{"type":"can-map-define._type"},{"type":"String"}]},{"name":"Type","description":"A constructor function that takes \nthe value passed to [can-map.prototype.attr attr] as the first argument and called with \nnew. For example, if you want whatever\ngets passed to go through `new Array(newValue)` you can do that like:\n\n define: {\n items: {\n Type: Array\n }\n }\n\nIf the value passed to [can-map.prototype.attr attr] is already an Array, it will be left as is.\n","types":[{"type":"can-map-define.TypeConstructor"}]},{"name":"set","description":"A set function that specifies what should happen when an attribute\nis set on a [can-map]. `set` is called with the result of `type` or `Type`. The following\ndefines a `page` setter that updates the map's offset:\n\n define: {\n page: {\n set: function(newVal){\n this.attr('offset', (parseInt(newVal) - 1) * \n this.attr('limit'));\n }\n }\n }\n","types":[{"type":"can-map-define.set"}]},{"name":"get","description":"A function that specifies how the value is retrieved. The get function is \nconverted to an [can-compute.async async compute]. It should derive its value from other values\non the map. The following\ndefines a `page` getter that reads from a map's offset and limit:\n\n define: {\n page: {\n get: function (newVal) {\n\t\t return Math.floor(this.attr('offset') / \n\t\t this.attr('limit')) + 1;\n\t\t}\n }\n }\n \nA `get` definition makes the property __computed__ which means it will not be serialized by default.\n","types":[{"type":"can-map-define.get"}]},{"name":"remove","description":"A function that specifies what should happen when an attribute is removed\nwith [can-map.prototype.removeAttr removeAttr]. The following removes a `modelId` when `makeId` is removed:\n\n define: {\n makeId: {\n remove: function(){\n this.removeAttr(\"modelId\");\n }\n }\n }\n","types":[{"type":"can-map-define.remove"}]},{"name":"serialize","description":"Specifies the behavior of the \nproperty when [can-map.prototype.serialize serialize] is called. \n\nBy default, serialize does not include computed values. Properties with a `get` definition\nare computed and therefore are not added to the result. Non-computed properties values are\nserialized if possible and added to the result.\n\n Paginate = Map.extend({\n define: {\n pageNum: {\n get: function(){ return this.offset() / 20 }\n }\n }\n });\n \n p = new Paginate({offset: 40});\n p.serialize() //-> {offset: 40}\n\nIf `true` is specified, computed properties will be serialized and added to the result.\n\n Paginate = Map.extend({\n define: {\n pageNum: { \n get: function(){ return this.offset() / 20 },\n serialize: true\n }\n }\n });\n\n p = new Paginate({offset: 40});\n p.serialize() //-> {offset: 40, pageNum: 2}\n \n \nIf `false` is specified, non-computed properties will not be added to the result.\n\n Paginate = Map.extend({\n define: {\n offset: {\n serialize: false\n }\n }\n });\n\n p = new Paginate({offset: 40});\n p.serialize() //-> {}\n\nIf a [can-map-define.serialize serialize function] is specified, the result\nof the function is added to the result.\n\n Paginate = Map.extend({\n define: {\n offset: {\n serialize: function(offset){\n return (offset / 20)+1\n }\n }\n }\n });\n\n p = new Paginate({offset: 40});\n p.serialize() //-> {offset: 3}\n \n","types":[{"type":"can-map-define.serialize"},{"type":"Boolean"}]}]}],"name":"can-map-define.attrDefinition","parent":"can-map-define","pathToRoot":".."}; </script> </article> <footer><p>CanJS is part of <a href="http://donejs.com" target="_blank">DoneJS</a>. Created and maintained by the core <a href="https://donejs.com/About.html#section=section_Team" target="_blank">DoneJS team</a> and <a href="http://bitovi.com" target="_blank">Bitovi</a>. <strong>Currently 3.0.0.</strong></p></footer> </div> </div> </div> <script> steal = { instantiated: { "bundles/bit-docs-site/static.css!$css" : null } }; </script> <script type='text/javascript' data-main="bit-docs-site/static" src="./static/node_modules/steal/steal.production.js"></script> <script async defer src="https://buttons.github.io/buttons.js"></script> </body> </html>