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<!DOCTYPE HTML>

<head>

<title>API overview | MobX</title>

</head>

<body>

</div>

Introduction

</a>

</li>

<span><b>1.</b> Introduction to MobX</span>

The Gist of MobX

</a>

</li>

Concepts & Principles

</a>

</li>

</ul>

</li>

API overview

</a>

</li>

<span><b>3.</b> Making things observable</span>

observable

</a>

</li>

@observable

</a>

</li>

objects

</a>

</li>

arrays

</a>

</li>

maps

</a>

</li>

boxed values

</a>

</li>

decorators

</a>

</li>

</ul>

</li>

<span><b>4.</b> Reacting to observables</span>

(@)computed

</a>

</li>

autorun

</a>

</li>

when

</a>

</li>

reaction

</a>

</li>

(@)observer

</a>

</li>

Understanding what MobX reacts to

</a>

</li>

</ul>

</li>

<span><b>5.</b> Changing observables</span>

action

</a>

</li>

async actions & flows

</a>

</li>

Object api

</a>

</li>

</ul>

</li>

<span><b>6.</b> Utility functions</span>

toJS

</a>

</li>

extendObservable

</a>

</li>

createAtom

</a>

</li>

intercept & observe

</a>

</li>

mobxUtils.fromPromise

</a>

</li>

mobxUtis.fromResource

</a>

</li>

mobxUtils.toStream

</a>

</li>

mobxUtils.fromStream

</a>

</li>

mobxUtils.now

</a>

</li>

mobxUtils.keepAlive

</a>

</li>

mobxUtils.createTransformer

</a>

</li>

mobxUtils.expr

</a>

</li>

</ul>

</li>

Blogs, videos, related projects

</a>

</li>

<span><b>8.</b> Tips & Tricks</span>

Frequently Asked Questions

</a>

</li>

Common Pitfalls & Best Practices

</a>

</li>

How to (not) use decorator syntax

</a>

</li>

Using trace for debugging

</a>

</li>

Defining data stores

</a>

</li>

Optimizing React components

</a>

</li>

DevTools

</a>

</li>

spy

</a>

</li>

</ul>

</li>

Donate

</a>

</li>

<li>

Published with GitBook

</a>

</li>

</ul>

</nav>

</div>

</a>

</div>

</div>

<button type="button" data-font="0" class="button">Serif</button>

</div>

<button type="button" id="color-theme-preview-0" class="button size-3" data-theme="0">White</button>

<button type="button" id="color-theme-preview-1" class="button size-3" data-theme="1">Sepia</button>

<button type="button" id="color-theme-preview-2" class="button size-3" data-theme="2">Night</button>

</div>

</a>

</div>

Share on Twitter

</button>

Share on Google

</button>

Share on Facebook

</button>

Share on Weibo

</button>

Share on Instapaper

</button>

</div>

<h1>

</h1>

</div>

<html><head></head><body><a id="edit-link" href="https://github.com/mobxjs/mobx/tree/gh-pages/docs/refguide/api.md" class="btn fa fa-edit pull-left">  Edit This Page</a><h1 id="mobx-api-reference"><a name="mobx-api-reference" class="plugin-anchor" href="#mobx-api-reference"><span class="fa fa-link"></span></a>MobX Api Reference</h1>

<p><strong>Applies to MobX 4 and higher</strong></p>

<ul>

<li>Using Mobx 3? Use this <a href="https://github.com/mobxjs/mobx/wiki/Migrating-from-mobx-3-to-mobx-4" target="_blank">migration guide</a> to switch gears.</li>

<li><a href="https://github.com/mobxjs/mobx/blob/54557dc319b04e92e31cb87427bef194ec1c549c/docs/refguide/api.md" target="_blank">MobX 3 documentation</a></li>

<li>For MobX 2, the old documentation is still available on <a href="https://github.com/mobxjs/mobx/blob/7c9e7c86e0c6ead141bb0539d33143d0e1f576dd/docs/refguide/api.md" target="_blank">github</a>.</li>

</ul>

<p><em>These are the most important MobX API's.</em></p>

<p>Understanding <code>observable</code>, <code>computed</code>, <code>reaction</code> and <code>action</code> is enough

to master MobX and use it in your applications!</p>

</blockquote>

<h2 id="creating-observables"><a name="creating-observables" class="plugin-anchor" href="#creating-observables"><span class="fa fa-link"></span></a>Creating observables</h2>

<h3 id="-observable-value"><a name="-observable-value" class="plugin-anchor" href="#-observable-value"><span class="fa fa-link"></span></a><code>observable(value)</code></h3>

<p>Usage:</p>

<ul>

<li><code>observable(value)</code></li>

<li><code>@observable classProperty = value</code></li>

</ul>

<p>Observable values can be JS primitives, references, plain objects, class instances, arrays and maps.</p>

<p><strong>Note:</strong> <code>observable(value)</code> is a convenience API that will succeed only if it can be made into

an observable data structure (<em>Array</em>, <em>Map</em>, or <em>observable-object</em>). For all other values, no conversion will be performed.</p>

<p>You can also directly create the desired observable type, see below.</p>

<p>The following conversion rules are applied, but can be fine-tuned by using <a href="#decorators"><em>decorators</em></a>. See below.</p>

<ol>

<li>If <em>value</em> is an instance of an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" target="_blank">ES6 Map</a>: a new <a href="map.html">Observable Map</a> will be returned. Observable maps are very useful if you don't want to react just to the change of a specific entry, but also to the addition or removal of entries.</li>

<li>If <em>value</em> is an array, a new <a href="array.html">Observable Array</a> will be returned.</li>

<li>If <em>value</em> is an object <em>without</em> prototype or its prototype is <code>Object.prototype</code>, the object will be cloned and all its current properties will be made observable. See <a href="object.html">Observable Object</a></li>

<li>If <em>value</em> is an object <em>with</em> a prototype, a JavaScript primitive or function, there will be no change made to the value. If you do need a <a href="boxed.html">Boxed Observable</a>, you can do one of the following:<ul>

<li>Call <code>observable.box(value)</code> explicitly</li>

<li>Use <code>@observable</code> in the class definition</li>

<li>Call <a href="#decorate"><code>decorate()</code></a></li>

<li>Use <code>extendObservable()</code> to introduce properties on a class definition</li>

</ul>

</li>

</ol>

<p>MobX will not make objects with a prototype automatically observable; as that is the responsibility of its constructor function. Use <code>extendObservable</code> in the constructor, or <code>@observable</code> in its class definition instead.</p>

<p>These rules might seem complicated at first sight, but you will notice that in practice they are very intuitive to work with.</p>

<p><strong>Some notes:</strong></p>

<ul>

<li>To create dynamically keyed objects, always use maps! Only initially existing properties on an object will be made observable, although new ones can be added using <code>extendObservable</code>.</li>

<li>To use the <code>@observable</code> decorator, make sure that <a href="http://mobxjs.github.io/mobx/refguide/observable-decorator.html" target="_blank">decorators are enabled</a> in your transpiler (babel or typescript).</li>

<li>By default making a data structure observable is <em>infective</em>; that means that <code>observable</code> is applied automatically to any value that is contained by the data structure, or will be contained by the data structure in the future. This behavior can be changed by using <a href="#decorators"><em>decorators</em></a>.</li>

</ul>

<p><a href="observable.html">«<code>observable</code>»</a> — <a href="observable-decorator.html">«<code>@observable</code>»</a></p>

<h3 id="-observable-property-value"><a name="-observable-property-value" class="plugin-anchor" href="#-observable-property-value"><span class="fa fa-link"></span></a><code>@observable property = value</code></h3>

<p><code>observable</code> can also be used as property decorator. It requires <a href="../best/decorators.html">decorators to be enabled</a> and is syntactic

sugar for <code>extendObservable(this, { property: value })</code>.</p>

<p><a href="observable-decorator.html">«<code>details</code>»</a></p>

<h3 id="-observable-box-value-options"><a name="-observable-box-value-options" class="plugin-anchor" href="#-observable-box-value-options"><span class="fa fa-link"></span></a><code>observable.box(value, options?)</code></h3>

<p>Creates an observable <em>box</em> that stores an observable reference to a value. Use <code>get()</code> to get the current value of the box, and <code>set()</code> to update it.

This is the foundation on which all other observables are built, but in practice you will use it rarely.</p>

<p>Normal boxes will automatically try to turn any new value into an observable if it isn't already. Use the <code>{deep: false}</code> option to disable this behavior.</p>

<p><a href="boxed.html">«<code>details</code>»</a></p>

<h3 id="-observable-object-value-decorators-options"><a name="-observable-object-value-decorators-options" class="plugin-anchor" href="#-observable-object-value-decorators-options"><span class="fa fa-link"></span></a><code>observable.object(value, decorators?, options?)</code></h3>

<p>Creates a clone of the provided object and makes all its properties observable.

By default any values in those properties will be made observable as well, but when using the <code>{deep: false}</code> options, only the properties will be made into observable

references, leaving the values untouched. (This holds also for any values assigned in the future).</p>

<p>The second argument in <code>observable.object()</code> can be used to fine tune the observability with <a href="#decorators"><code>decorators</code></a>.</p>

<p><a href="object.html">«<code>details</code>»</a>the</p>

<h3 id="-observable-array-value-options"><a name="-observable-array-value-options" class="plugin-anchor" href="#-observable-array-value-options"><span class="fa fa-link"></span></a><code>observable.array(value, options?)</code></h3>

<p>Creates a new observable array based on the provided value.</p>

<p>Use the <code>{deep: false}</code> option if the values in the array should not be turned into observables.</p>

<p><a href="array.html">«<code>details</code>»</a></p>

<h3 id="-observable-map-value-options"><a name="-observable-map-value-options" class="plugin-anchor" href="#-observable-map-value-options"><span class="fa fa-link"></span></a><code>observable.map(value, options?)</code></h3>

<p>Creates a new observable map based on the provided value. Use the <code>{deep: false}</code> option if the values in the map should not be turned into observables.</p>

<p>Use <code>map</code> whenever you want to create a dynamically keyed collections and the addition / removal of keys needs to be observed.

Since this uses the full-blown <em>ES6 Map</em> internally, you are free to use any type for the key and <em>not limited</em> to string keys.</p>

<p><a href="map.html">«<code>details</code>»</a></p>

<h3 id="-extendobservable"><a name="-extendobservable" class="plugin-anchor" href="#-extendobservable"><span class="fa fa-link"></span></a><code>extendObservable</code></h3>

<p>Usage: <code>extendObservable(target, properties, decorators?, options?)</code>.</p>

<p>For each key/value pair in each <code>propertyMap</code> a (new) observable property will be introduced on the target object.

This can be used in constructor functions to introduce observable properties without using decorators.

If a value of the <code>propertyMap</code> is a getter function, a <em>computed</em> property will be introduced.</p>

<p>Use <code>extendObservable(target, props, decorators?, {deep: false})</code> if the new properties should not be infective (that is; newly assigned values should not be turned into observables automatically).

Note that <code>extendObservable</code> enhances existing objects, unlike <code>observable.object</code> which creates a new object.</p>

<p><a href="extend-observable.html">«details»</a></p>

<h3 id="decorators"><a name="decorators" class="plugin-anchor" href="#decorators"><span class="fa fa-link"></span></a>Decorators</h3>

<p>Use decorators to fine tune the observability of properties defined via <code>observable</code>, <code>extendObservable</code> and <code>observable.object</code>. They can also control the auto-conversion rules for specific properties.</p>

<p>The following decorators are available:</p>

<ul>

<li><strong><code>observable.deep</code></strong>: This is the default decorator, used by any observable. It converts any assigned, non-primitive value into an observable if it isn't one yet.</li>

<li><strong><code>observable.ref</code></strong>: Disables automatic observable conversion, just creates an observable reference instead.</li>

<li><strong><code>observable.shallow</code></strong>: Can only be used in combination with collections. Turns any assigned collection into an collection, which is shallowly observable (instead of deep). In other words; the values inside the collection won't become observables automatically.</li>

<li><strong><code>computed</code></strong>: Creates a derived property, see <a href="computed-decorator.html"><code>computed</code></a></li>

<li><strong><code>action</code></strong>: Creates an action, see <a href="action.html"><code>action</code></a></li>

<li><strong><code>action.bound</code></strong>: Creates a bound action, see <a href="action.html"><code>action</code></a></li>

</ul>

<p>You can apply these decorators using the <em>@decorator</em> syntax:</p>

<pre><code class="lang-javascript"><span class="hljs-keyword">import</span> {observable, action} <span class="hljs-keyword">from</span> <span class="hljs-string">'mobx'</span>;

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">TaskStore</span> </span>{

@observable.shallow tasks = []

@action addTask(task) { <span class="hljs-comment">/* ... */</span> }

}

</code></pre>

<p>Or by passing in property decorators via <code>observable.object</code> / <code>observable.extendObservable</code> or <a href="#decorate"><code>decorate()</code></a>.

Note that decorators always 'stick' to the property. So they will remain in effect even if a new value is assigned.</p>

<pre><code class="lang-javascript"><span class="hljs-keyword">import</span> {observable, action} <span class="hljs-keyword">from</span> <span class="hljs-string">'mobx'</span>;

<span class="hljs-keyword">const</span> taskStore = observable({

tasks: [],

addTask(task) { <span class="hljs-comment">/* ... */</span> }

}, {

tasks: observable.shallow,

addTask: action

})

</code></pre>

<p><a href="modifiers.html">«details»</a></p>

<h3 id="-decorate"><a name="-decorate" class="plugin-anchor" href="#-decorate"><span class="fa fa-link"></span></a><code>decorate</code></h3>

<p>Usage: <code>decorate(object, decorators)</code>

This is a convenience method to apply observability <a href="#decorators">decorators</a> to the properties of a plain object or class instance. The second argument is an object with properties set to certain decorators.</p>

<p>Use this if you cannot use the <em>@decorator</em> syntax or need more control over setting observability.</p>

<pre><code class="lang-js"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">TodoList</span> </span>{

todos = {}

get unfinishedTodoCount() {

<span class="hljs-keyword">return</span> values(<span class="hljs-keyword">this</span>.todos).filter(todo => !todo.finished).length

}

addTodo() {

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