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<!DOCTYPE HTML>
<html lang="en" >
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<title>API overview | MobX</title>
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</head>
<body>
<div class="book"
data-level="2"
data-chapter-title="API overview"
data-filepath="refguide/api.md"
data-basepath=".."
data-revision="Fri Nov 30 2018 16:57:29 GMT+0100 (CET)"
data-innerlanguage="">
<div class="book-summary">
<nav role="navigation">
<ul class="summary">
<li class="chapter " data-level="0" data-path="index.html">
<a href="../index.html">
<i class="fa fa-check"></i>
Introduction
</a>
</li>
<li class="chapter " data-level="1" >
<span><b>1.</b> Introduction to MobX</span>
<ul class="articles">
<li class="chapter " data-level="1.1" data-path="intro/overview.html">
<a href="../intro/overview.html">
<i class="fa fa-check"></i>
<b>1.1.</b>
The Gist of MobX
</a>
</li>
<li class="chapter " data-level="1.2" data-path="intro/concepts.html">
<a href="../intro/concepts.html">
<i class="fa fa-check"></i>
<b>1.2.</b>
Concepts & Principles
</a>
</li>
</ul>
</li>
<li class="chapter active" data-level="2" data-path="refguide/api.html">
<a href="../refguide/api.html">
<i class="fa fa-check"></i>
<b>2.</b>
API overview
</a>
</li>
<li class="chapter " data-level="3" >
<span><b>3.</b> Making things observable</span>
<ul class="articles">
<li class="chapter " data-level="3.1" data-path="refguide/observable.html">
<a href="../refguide/observable.html">
<i class="fa fa-check"></i>
<b>3.1.</b>
observable
</a>
</li>
<li class="chapter " data-level="3.2" data-path="refguide/observable-decorator.html">
<a href="../refguide/observable-decorator.html">
<i class="fa fa-check"></i>
<b>3.2.</b>
@observable
</a>
</li>
<li class="chapter " data-level="3.3" data-path="refguide/object.html">
<a href="../refguide/object.html">
<i class="fa fa-check"></i>
<b>3.3.</b>
objects
</a>
</li>
<li class="chapter " data-level="3.4" data-path="refguide/array.html">
<a href="../refguide/array.html">
<i class="fa fa-check"></i>
<b>3.4.</b>
arrays
</a>
</li>
<li class="chapter " data-level="3.5" data-path="refguide/map.html">
<a href="../refguide/map.html">
<i class="fa fa-check"></i>
<b>3.5.</b>
maps
</a>
</li>
<li class="chapter " data-level="3.6" data-path="refguide/boxed.html">
<a href="../refguide/boxed.html">
<i class="fa fa-check"></i>
<b>3.6.</b>
boxed values
</a>
</li>
<li class="chapter " data-level="3.7" data-path="refguide/modifiers.html">
<a href="../refguide/modifiers.html">
<i class="fa fa-check"></i>
<b>3.7.</b>
decorators
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="4" >
<span><b>4.</b> Reacting to observables</span>
<ul class="articles">
<li class="chapter " data-level="4.1" data-path="refguide/computed-decorator.html">
<a href="../refguide/computed-decorator.html">
<i class="fa fa-check"></i>
<b>4.1.</b>
(@)computed
</a>
</li>
<li class="chapter " data-level="4.2" data-path="refguide/autorun.html">
<a href="../refguide/autorun.html">
<i class="fa fa-check"></i>
<b>4.2.</b>
autorun
</a>
</li>
<li class="chapter " data-level="4.3" data-path="refguide/when.html">
<a href="../refguide/when.html">
<i class="fa fa-check"></i>
<b>4.3.</b>
when
</a>
</li>
<li class="chapter " data-level="4.4" data-path="refguide/reaction.html">
<a href="../refguide/reaction.html">
<i class="fa fa-check"></i>
<b>4.4.</b>
reaction
</a>
</li>
<li class="chapter " data-level="4.5" data-path="refguide/observer-component.html">
<a href="../refguide/observer-component.html">
<i class="fa fa-check"></i>
<b>4.5.</b>
(@)observer
</a>
</li>
<li class="chapter " data-level="4.6" data-path="best/react.html">
<a href="../best/react.html">
<i class="fa fa-check"></i>
<b>4.6.</b>
Understanding what MobX reacts to
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="5" >
<span><b>5.</b> Changing observables</span>
<ul class="articles">
<li class="chapter " data-level="5.1" data-path="refguide/action.html">
<a href="../refguide/action.html">
<i class="fa fa-check"></i>
<b>5.1.</b>
action
</a>
</li>
<li class="chapter " data-level="5.2" data-path="best/actions.html">
<a href="../best/actions.html">
<i class="fa fa-check"></i>
<b>5.2.</b>
async actions & flows
</a>
</li>
<li class="chapter " data-level="5.3" data-path="refguide/object-api.html">
<a href="../refguide/object-api.html">
<i class="fa fa-check"></i>
<b>5.3.</b>
Object api
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="6" >
<span><b>6.</b> Utility functions</span>
<ul class="articles">
<li class="chapter " data-level="6.1" data-path="refguide/tojson.html">
<a href="../refguide/tojson.html">
<i class="fa fa-check"></i>
<b>6.1.</b>
toJS
</a>
</li>
<li class="chapter " data-level="6.2" data-path="refguide/extend-observable.html">
<a href="../refguide/extend-observable.html">
<i class="fa fa-check"></i>
<b>6.2.</b>
extendObservable
</a>
</li>
<li class="chapter " data-level="6.3" data-path="refguide/extending.html">
<a href="../refguide/extending.html">
<i class="fa fa-check"></i>
<b>6.3.</b>
createAtom
</a>
</li>
<li class="chapter " data-level="6.4" data-path="refguide/observe.html">
<a href="../refguide/observe.html">
<i class="fa fa-check"></i>
<b>6.4.</b>
intercept & observe
</a>
</li>
<li class="chapter " data-level="6.5" >
<a target="_blank" href="https://github.com/mobxjs/mobx-utils#frompromise">
<i class="fa fa-check"></i>
<b>6.5.</b>
mobxUtils.fromPromise
</a>
</li>
<li class="chapter " data-level="6.6" >
<a target="_blank" href="https://github.com/mobxjs/mobx-utils#fromresource">
<i class="fa fa-check"></i>
<b>6.6.</b>
mobxUtils.fromResource
</a>
</li>
<li class="chapter " data-level="6.7" >
<a target="_blank" href="https://github.com/mobxjs/mobx-utils#tostream">
<i class="fa fa-check"></i>
<b>6.7.</b>
mobxUtils.toStream
</a>
</li>
<li class="chapter " data-level="6.8" >
<a target="_blank" href="https://github.com/mobxjs/mobx-utils#fromstream">
<i class="fa fa-check"></i>
<b>6.8.</b>
mobxUtils.fromStream
</a>
</li>
<li class="chapter " data-level="6.9" >
<a target="_blank" href="https://github.com/mobxjs/mobx-utils#now">
<i class="fa fa-check"></i>
<b>6.9.</b>
mobxUtils.now
</a>
</li>
<li class="chapter " data-level="6.10" data-path="refguide/create-transformer.html">
<a href="../refguide/create-transformer.html">
<i class="fa fa-check"></i>
<b>6.10.</b>
mobxUtils.createTransformer
</a>
</li>
<li class="chapter " data-level="6.11" data-path="refguide/expr.html">
<a href="../refguide/expr.html">
<i class="fa fa-check"></i>
<b>6.11.</b>
mobxUtils.expr
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="7" >
<a target="_blank" href="https://github.com/mobxjs/awesome-mobx#examples">
<i class="fa fa-check"></i>
<b>7.</b>
Blogs, videos, related projects
</a>
</li>
<li class="chapter " data-level="8" >
<span><b>8.</b> Tips & Tricks</span>
<ul class="articles">
<li class="chapter " data-level="8.1" data-path="faq/faq.html">
<a href="../faq/faq.html">
<i class="fa fa-check"></i>
<b>8.1.</b>
Frequently Asked Questions
</a>
</li>
<li class="chapter " data-level="8.2" data-path="best/pitfalls.html">
<a href="../best/pitfalls.html">
<i class="fa fa-check"></i>
<b>8.2.</b>
Common Pitfalls & Best Practices
</a>
</li>
<li class="chapter " data-level="8.3" data-path="best/decorators.html">
<a href="../best/decorators.html">
<i class="fa fa-check"></i>
<b>8.3.</b>
How to (not) use decorator syntax
</a>
</li>
<li class="chapter " data-level="8.4" data-path="best/trace.html">
<a href="../best/trace.html">
<i class="fa fa-check"></i>
<b>8.4.</b>
Using trace for debugging
</a>
</li>
<li class="chapter " data-level="8.5" data-path="best/store.html">
<a href="../best/store.html">
<i class="fa fa-check"></i>
<b>8.5.</b>
Defining data stores
</a>
</li>
<li class="chapter " data-level="8.6" data-path="best/react-performance.html">
<a href="../best/react-performance.html">
<i class="fa fa-check"></i>
<b>8.6.</b>
Optimizing React components
</a>
</li>
<li class="chapter " data-level="8.7" data-path="best/devtools.html">
<a href="../best/devtools.html">
<i class="fa fa-check"></i>
<b>8.7.</b>
DevTools
</a>
</li>
<li class="chapter " data-level="8.8" data-path="refguide/spy.html">
<a href="../refguide/spy.html">
<i class="fa fa-check"></i>
<b>8.8.</b>
spy
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="9" data-path="donating.html">
<a href="../donating.html">
<i class="fa fa-check"></i>
<b>9.</b>
Donate
</a>
</li>
<li class="divider"></li>
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Published with GitBook
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<div class="book-body">
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<!-- Actions Left -->
<!-- Title -->
<h1>
<i class="fa fa-circle-o-notch fa-spin"></i>
<a href="../" >MobX</a>
</h1>
</div>
<div class="page-wrapper" tabindex="-1" role="main">
<div class="page-inner">
<section class="normal" id="section-">
<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>
<h1 id="core-api"><a name="core-api" class="plugin-anchor" href="#core-api"><span class="fa fa-link"></span></a>Core API</h1>
<p><em>These are the most important MobX API's.</em></p>
<blockquote>
<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="observablevalue"><a name="observablevalue" class="plugin-anchor" href="#observablevalue"><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 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>
<li><em>[MobX 4 and below]</em> 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>
</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="observableboxvalue-options"><a name="observableboxvalue-options" class="plugin-anchor" href="#observableboxvalue-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="observableobjectvalue-decorators-options"><a name="observableobjectvalue-decorators-options" class="plugin-anchor" href="#observableobjectvalue-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></p>
<h3 id="observablearrayvalue-options"><a name="observablearrayvalue-options" class="plugin-anchor" href="#observablearrayvalue-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="observablemapvalue-options"><a name="observablemapvalue-options" class="plugin-anchor" href="#observablemapvalue-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 a 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() {
<span class="hljs-keyword">const</span> t = <span class="hljs-keyword">new</span> Todo()
t.title = <span class="hljs-string">'Test_'</span> + <span class="hljs-built_in">Math</span>.random()
set(<span class="hljs-keyword">this</span>.todos, t.id, t)
}
}
decorate(TodoList, {
todos: observable,
unfinishedTodoCount: computed,
addTodo: action.bound
})
</code></pre>
<p>For applying multiple decorators on a single property, you can pass an array of decorators. The decorators application order is from right to left.</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">import</span> { decorate, observable } <span class="hljs-keyword">from</span> <span class="hljs-string">'mobx'</span>
<span class="hljs-keyword">import</span> { serializable, primitive } <span class="hljs-keyword">from</span> <span class="hljs-string">'serializr'</span>
<span class="hljs-keyword">import</span> persist <span class="hljs-keyword">from</span> <span class="hljs-string">'mobx-persist'</span>
class Todo {
id = Math.random();
title = <span class="hljs-string">''</span>;
finished = <span class="hljs-literal">false</span>;
}
decorate(Todo, {
title: [serializable(primitive), persist(<span class="hljs-string">'object'</span>), observable],
finished: [serializable(primitive), observable]
})
</code></pre>
<p>Note: Not all decorators can be composed together, and this functionality is just best-effort. Some decorators affect the instance directly and can 'hide' the effect of other decorators that only change the prototype.</p>
<h2 id="computed-values"><a name="computed-values" class="plugin-anchor" href="#computed-values"><span class="fa fa-link"></span></a>Computed values</h2>
<p>Usage:</p>
<ul>
<li><code>computed(() => expression)</code></li>
<li><code>computed(() => expression, (newValue) => void)</code></li>
<li><code>computed(() => expression, options)</code></li>
<li><code>@computed get classProperty() { return expression; }</code></li>
<li><code>@computed({equals: compareFn}) get classProperty() { return expression; }</code></li>
<li><code>@computed.struct get classProperty() { return expression; }</code></li>
</ul>
<p>Creates a computed property. The <code>expression</code> should not have side effects but return a value.
The expression will automatically be re-evaluated if any observables it uses changes, but only if it is in use by some <em>reaction</em>.</p>
<p>There are various <code>options</code> that can be used to control the behavior of <code>computed</code>. These include:</p>
<ul>
<li><strong><code>equals: (value, value) => boolean</code></strong> Comparison method can be used to override the default detection on when something is changed. Built-in comparers are: <code>comparer.identity</code>, <code>comparer.default</code>, <code>comparer.structural</code>.</li>
<li><strong><code>name: string</code></strong> Provide a debug name to this computed property</li>
<li><strong><code>requiresReaction: boolean</code></strong> Wait for a change in value of the tracked observables, before recomputing the derived property</li>
<li><strong><code>get: () => value)</code></strong> Override the getter for the computed property.</li>
<li><strong><code>set: (value) => void</code></strong> Override the setter for the computed property</li>
<li><strong><code>keepAlive: boolean</code></strong> Set to true to automatically keep computed values alive, rather then suspending then when there are no observers.</li>
</ul>
<p><a href="computed-decorator.html">«details»</a></p>
<h2 id="actions"><a name="actions" class="plugin-anchor" href="#actions"><span class="fa fa-link"></span></a>Actions</h2>
<p>Any application has actions. Actions are anything that modify the state.</p>
<p>With MobX you can make it explicit in your code where your actions live by marking them.
Actions helps you to structure your code better.
It is advised to use them on any function that modifies observables or has side effects.
<code>action</code> also provides useful debugging information in combination with the devtools.
Note: using <code>action</code> is mandatory when <em>strict mode</em> is enabled, see <code>enforceActions</code>.
<a href="action.html">«details»</a></p>
<p>Usage:</p>
<ul>
<li><code>action(fn)</code></li>
<li><code>action(name, fn)</code></li>
<li><code>@action classMethod</code></li>
<li><code>@action(name) classMethod</code></li>
<li><code>@action boundClassMethod = (args) => { body }</code></li>
<li><code>@action.bound boundClassMethod(args) { body }</code></li>
</ul>
<p>For one-time-actions <code>runInAction(name?, fn)</code> can be used, which is sugar for <code>action(name, fn)()</code>.</p>
<h3 id="flow"><a name="flow" class="plugin-anchor" href="#flow"><span class="fa fa-link"></span></a>Flow</h3>
<p>Usage: <code>flow(function* (args) { })</code></p>
<p><code>flow()</code> takes a generator function as its only input</p>
<p>When dealing with <em>async actions</em>, the code that executes in the callback is not wrapped by <code>action</code>. This means the observable state that you are mutating, will fail the <a href="#configure"><code>enforceActions</code></a> check. An easy way to retain the action semantics is by wrapping the async function with flow. This will ensure to wrap all your callbacks in <code>action()</code>.</p>
<p>Note that the async function must be a <em>generator</em> and you must only <em>yield</em> to promises inside. <code>flow</code> gives you back a promise that you can <code>cancel()</code> if you want.</p>
<pre><code class="lang-js"><span class="hljs-keyword">import</span> { configure } <span class="hljs-keyword">from</span> <span class="hljs-string">'mobx'</span>;
<span class="hljs-comment">// don't allow state modifications outside actions</span>