mobx-react

What is mobx-react?

The mobx-react package provides React bindings for MobX, a state management library. It allows you to connect your React components to MobX observables, making it easier to manage and react to state changes in your application.

What are mobx-react's main functionalities?

Observer Component

The observer function is used to create a reactive component that will automatically re-render when the observed state changes.

import React from 'react';
import { observer } from 'mobx-react';
import { observable } from 'mobx';

const appState = observable({
  count: 0
});

const Counter = observer(() => (
  <div>
    <button onClick={() => appState.count++}>Increment</button>
    <p>{appState.count}</p>
  </div>
));

export default Counter;

Injecting Stores

The inject function is used to inject stores into components, making it easier to access MobX stores within your React components.

import React from 'react';
import { Provider, inject, observer } from 'mobx-react';
import { observable } from 'mobx';

class Store {
  @observable count = 0;
}

const store = new Store();

const Counter = inject('store')(observer(({ store }) => (
  <div>
    <button onClick={() => store.count++}>Increment</button>
    <p>{store.count}</p>
  </div>
)));

const App = () => (
  <Provider store={store}>
    <Counter />
  </Provider>
);

export default App;

Using MobX with React Hooks

The useLocalObservable hook is used to create local observable state within a functional component, allowing you to use MobX with React hooks.

import React from 'react';
import { useLocalObservable, observer } from 'mobx-react';

const Counter = observer(() => {
  const state = useLocalObservable(() => ({
    count: 0,
    increment() {
      this.count++;
    }
  }));

  return (
    <div>
      <button onClick={state.increment}>Increment</button>
      <p>{state.count}</p>
    </div>
  );
});

export default Counter;

Other packages similar to mobx-react

redux

Redux is a popular state management library for JavaScript applications. Unlike MobX, which uses observables and decorators, Redux relies on a single immutable state tree and pure reducer functions to manage state. Redux is often used with the react-redux bindings to connect React components to the Redux store.

recoil

Recoil is a state management library for React that provides a more fine-grained approach to state management compared to Redux. It allows you to create atoms and selectors to manage state and derive state. Recoil is designed to work seamlessly with React's concurrent mode and hooks.

zustand

Zustand is a small, fast, and scalable state management library for React. It uses hooks to create and manage state, providing a simple and intuitive API. Unlike MobX, which uses observables, Zustand relies on React's built-in state management capabilities.

README

mobx-react

Package with react component wrapper for combining React with mobx. Exports the observer decorator and some development utilities. For documentation, see the mobx project. This package supports both React and React-Native.

Installation

npm install mobx-react --save

import {observer} from 'mobx-react';
// - or -
import {observer} from 'mobx-react/native';
// - or, for custom renderers without DOM: -
import {observer} from 'mobx-react/custom';

This package provides the bindings for MobX and React. See the official documentation for how to get started.

Boilerplate projects that use mobx-react

• Minimal MobX, React, ES6, JSX, Hot reloading: MobX-React-Boilerplate
• TodoMVC MobX, React, ES6, JSX, Hot reloading: MobX-React-TodoMVC
• Minimal MobX, React, Typescript, TSX: MobX-React-Typescript-Boilerplate
• Minimal MobX, React, ES6(babel), JSPM with hot reloading modules: jspm-react
• React-Native Counter: Mobx-React-Native-Counter

API documentation

observer(componentClass)

Function (and decorator) that converts a React component definition, React component class or stand-alone render function into a reactive component. See the mobx documentation for more details.

import {observer} from "mobx-react";

// ---- ES5 syntax ----

const TodoView = observer(React.createClass({
    displayName: "TodoView",
    render() {
        return <div>{this.props.todo.title}</div>   
    }
}));

// ---- ES6 syntax ----

@observer class TodoView extends React.Component {
    render() {
        return <div>{this.props.todo.title}</div>   
    }   
}

// ---- or just use a stateless component function: ----

const TodoView = observer(({todo}) => <div>{todo.title}</div>)

It is possible to set a custom shouldComponentUpdate, but in general this should be avoid as MobX will by default provide a highly optimized shouldComponentUpdate implementation, based on PureRenderMixin. If a custom shouldComponentUpdate is provided, it is consulted when the props changes (because the parent passes new props) or the state changes (as a result of calling setState), but if an observable used by the rendering is changed, the component will be re-rendered and shouldComponent is not consulted.

componentWillReact (lifecycle hook)

React components usually render on a fresh stack, so that makes it often hard to figure out what caused a component to re-render. When using mobx-react you can define a new life cycle hook, componentWillReact (pun intended) that will be triggered when a component will be scheduled to re-render because data it observes has changed. This makes it easy to trace renders back to the action that caused the rendering.

import {observer} from "mobx-react";

@observer class TodoView extends React.Component {
    componentWillReact() {
        console.log("I will re-render, since the todo has changed!");    
    }

    render() {
        return <div>{this.props.todo.title}</div>   
    }   
}

• componentWillReact doesn't take arguments
• componentWillReact won't fire before the initial render (use componentWillMount instead)
• componentWillReact won't fire when receiving new props or after setState calls (use componentWillUpdate instead)

propTypes

MobX-react provides the following additional propTypes which can be used to validate against MobX structures:

• observableArray
• observableArrayOf(React.PropTypes.number)
• observableMap
• observableObject
• arrayOrObservableArray
• arrayOrObservableArrayOf(React.PropTypes.number)
• objectOrObservableObject

Provider and inject (Experimental)

This feature is marked as experimental as the exact api might change in a next minor, pending any community feedback.

Provider is a component that can pass stores (or other stuff) using React's context mechanism to child components. This is useful if you have things that you don't want to pass through multiple layers of components explicitly.

inject can be used to pick up those stores. It is a higher order component that takes a list of strings and makes those stores available to the wrapped component.

Example (based on the official context docs):

@inject("color") @observer
class Button extends React.Component {
  render() {
    return (
      <button style={{background: this.props.color}}>
        {this.props.children}
      </button>
    );
  }
}

class Message extends React.Component {
  render() {
    return (
      <div>
        {this.props.text} <Button>Delete</Button>
      </div>
    );
  }
}

class MessageList extends React.Component {
  render() {
    const children = this.props.messages.map((message) =>
      <Message text={message.text} />
    );
    return <Provider color="red">
        <div>
            {children}
        </div>
    </Provider>;
  }
}

Notes:

• If a component asks for a store and receives a store via a property with the same name, the property takes precedence. Use this to your advantage when testing!
• Values provided through Provider should be final, to avoid issues like mentioned in React #2517 and React #3973, where optimizations might stop the propagation of new context. Instead, make sure that if you put things in context that might change over time, that they are @observable or provide some other means to listen to changes, like callbacks.
• When using both @inject and @observer, make sure to apply them in the correct order: observer should be the inner decorator, inject the outer. There might be additional decorators in between.
• The original component wrapped by inject is available as the wrappedComponent property of created the higher order component.

Inject as function

The above example in ES5 would start like:

var Button = inject("color")(observer(React.createClass({
    /* ... etc ... */ 
})))

Strongly typing inject

inject also accepts a function ((allStores, nextProps, nextContext) => nextProps) that can be used to pick all the desired stores from the available stores like this:

import {IUserStore} from "myStore"

@inject((allStores) => ({
    userStore: allStores.userStore as IUserStore
}))
class MyComponent extends React.Component<{ userStore?: IUserStore; otherProp: number }, {}> {
    /* etc */
}

Make sure to mark userStore as optional property. It should not (necessarily) be passed in by parent components after all!

FAQ

Should I use observer for each component?

You should use observer on every component that displays observable data. Even the small ones. observer allows components to render independently from their parent and in general this means that the more you use observer, the better the performance become. The overhead of observer itself is neglectable. See also Do child components need @observer?

I see React warnings about forceUpdate / setState from React

The following warning will appear if you trigger a re-rendering between instantiating and rendering a component:

Warning: forceUpdate(...): Cannot update during an existing state transition (such as within `render`). Render methods should be a pure function of props and state.`

-- or --

Warning: setState(...): Cannot update during an existing state transition (such as within `render` or another component's constructor). Render methods should be a pure function of props and state; constructor side-effects are an anti-pattern, but can be moved to `componentWillMount`.

Usually this means that (another) component is trying to modify observables used by this components in their constructor or getInitialState methods. This violates the React Lifecycle, componentWillMount should be used instead if state needs to be modified before mounting.

Internal DevTools Api

trackComponents()

Enables the tracking from components. Each rendered reactive component will be added to the componentByNodeRegistery and its renderings will be reported through the renderReporter event emitter.

renderReporter

Event emitter that reports render timings and component destructions. Only available after invoking trackComponents(). New listeners can be added through renderReporter.on(function(data) { /* */ }).

Data will have one of the following formats:

{
    event: 'render',
    renderTime: /* time spend in the .render function of a component, in ms. */,
    totalTime: /* time between starting a .render and flushing the changes to the DOM, in ms. */,
    component: /* component instance */,
    node: /* DOM node */
}

{
    event: 'destroy',
    component: /* component instance */,
    node: /* DOM Node */
}

componentByNodeRegistery

WeakMap. Its get function returns the associated reactive component of the given node. The node needs to be precisely the root node of the component. This map is only available after invoking trackComponents.