Installation

MobX works in any ES5 environment, which includes browsers and NodeJS.

There are three types of React bindings:

mobx-react-lite. Utilities to manually apply observation
mobx-react-observer. Babel/swc plugin to automatically apply observation to components
mobx-react. Support for class components

Append the appropriate bindings for your use case to the Yarn or NPM command below:

Yarn: yarn add mobx

NPM: npm install --save mobx

CDN: https://cdnjs.com/libraries/mobx / https://unpkg.com/mobx/dist/mobx.umd.production.min.js

Transpilation settings

MobX and Decorators

Based on your preference, MobX can be used with or without decorators. Both the legacy implementation and the standardised TC-39 version of decorators are currently supported. See enabling-decorators for more details on how to enable them. Legacy decorator support will be removed in MobX 7, in favor of the standard.

Use spec compliant transpilation for class properties

When using MobX with TypeScript or Babel, and you plan to use classes; make sure to update your configuration to use a TC-39 spec compliant transpilation for class fields, since this is not always the default. Without this, class fields cannot be made observable before they are initialized.

TypeScript: Set the compiler option "useDefineForClassFields": true.

Babel: Make sure to use at least version 7.12, with the following configuration:

{
    // Babel < 7.13.0
    "plugins": [["@babel/plugin-proposal-class-properties", { "loose": false }]],

    // Babel >= 7.13.0 (https://babeljs.io/docs/en/assumptions)
    "plugins": [["@babel/plugin-proposal-class-properties"]],
    "assumptions": {
        "setPublicClassFields": false
    }
}

For verification insert this piece of code at the beginning of your sources (eg. index.js)

if (!new class { x }().hasOwnProperty('x')) throw new Error('Transpiler is not configured correctly');

MobX on older JavaScript environments

By default, MobX uses proxies for optimal performance and compatibility. However, on older JavaScript engines Proxy is not available (check out Proxy support). Examples of such are Internet Explorer (before Edge), Node.js < 6, iOS < 10, Android before RN 0.59, or Android on iOS.

In such cases, MobX can fallback to an ES5 compatible implementation which works almost identically, although there are a few limitations without Proxy support. You will have to explicitly enable the fallback implementation by configuring useProxies:

import { configure } from "mobx"

configure({ useProxies: "never" }) // Or "ifavailable".

This option will be removed in MobX 7.

MobX on other frameworks / platforms

MobX.dart: MobX for Flutter / Dart
lit-mobx: MobX for lit-element
mobx-angular: MobX for angular
mobx-vue: MobX for Vue