MobX

Simple, scalable state management.

---

Documentation for older unsupported V4/V5 can be found here, but be sure to read about current documentation first.

MobX is made possible by the generosity of the sponsors below, and many other individual backers. Sponsoring directly impacts the longevity of this project.

🥇Gold sponsors ($3000+ total contribution):

🥈Silver sponsors ($100+ pm):

🥉Bronze sponsors ($500+ total contributions):

---

Introduction

Anything that can be derived from the application state, should be. Automatically.

MobX is a battle tested library that makes state management simple and scalable by transparently applying functional reactive programming (TFRP). The philosophy behind MobX is simple:

😙

Straightforward

Write minimalistic, boilerplate free code that captures your intent. Trying to update a record field? Use the good old JavaScript assignment. Updating data in an asynchronous process? No special tools are required, the reactivity system will detect all your changes and propagate them out to where they are being used.

🚅

Effortless optimal rendering

All changes to and uses of your data are tracked at runtime, building a dependency tree that captures all relations between state and output. This guarantees that computations depending on your state, like React components, run only when strictly needed. There is no need to manually optimize components with error-prone and sub-optimal techniques like memoization and selectors.

🤹🏻‍♂️

Architectural freedom

MobX is unopinionated and allows you to manage your application state outside of any UI framework. This makes your code decoupled, portable, and above all, easily testable.

A quick example

So what does code that uses MobX look like?

import React from "react"
import ReactDOM from "react-dom"
import { makeAutoObservable } from "mobx"
import { observer } from "mobx-react"

// Model the application state.
class Timer {
    secondsPassed = 0

    constructor() {
        makeAutoObservable(this)
    }

    increase() {
        this.secondsPassed += 1
    }

    reset() {
        this.secondsPassed = 0
    }
}

const myTimer = new Timer()

// Build a "user interface" that uses the observable state.
const TimerView = observer(({ timer }) => (
    <button onClick={() => timer.reset()}>Seconds passed: {timer.secondsPassed}</button>
))

ReactDOM.render(<TimerView timer={myTimer} />, document.body)

// Update the 'Seconds passed: X' text every second.
setInterval(() => {
    myTimer.increase()
}, 1000)

The observer wrapper around the TimerView React component, will automatically detect that rendering depends on the timer.secondsPassed observable, even though this relationship is not explicitly defined. The reactivity system will take care of re-rendering the component when precisely that field is updated in the future.

Every event (onClick / setInterval) invokes an action (myTimer.increase / myTimer.reset) that updates observable state (myTimer.secondsPassed). Changes in the observable state are propagated precisely to all computations and side effects (TimerView) that depend on the changes being made.

This conceptual picture can be applied to the above example, or any other application using MobX.

To learn about the core concepts of MobX using a larger example, check out The gist of MobX section, or take the 10 minute interactive introduction to MobX and React. The philosophy and benefits of the mental model provided by MobX are also described in great detail in the blog posts UI as an afterthought and How to decouple state and UI (a.k.a. you don’t need componentWillMount).

Download the MobX 6 cheat sheet

What others are saying...

Guise, #mobx isn't pubsub, or your grandpa's observer pattern. Nay, it is a carefully orchestrated observable dimensional portal fueled by the power cosmic. It doesn't do change detection, it's actually a level 20 psionic with soul knife, slashing your viewmodel into submission.

After using #mobx for lone projects for a few weeks, it feels awesome to introduce it to the team. Time: 1/2, Fun: 2X

Working with #mobx is basically a continuous loop of me going “this is way too simple, it definitely won’t work” only to be proven wrong

I have built big apps with MobX already and comparing to the one before that which was using Redux, it is simpler to read and much easier to reason about.

The #mobx is the way I always want things to be! It's really surprising simple and fast! Totally awesome! Don't miss it!

Further resources and documentation

• MobX cheat sheet (also sponsors the project)
• 10 minute interactive introduction to MobX and React
• Egghead.io course, based on MobX 3

The MobX book

Created by Pavan Podila and Michel Weststrate.

Videos

• Introduction to MobX & React in 2020 by Leigh Halliday, 17min.
• ReactNext 2016: Real World MobX by Michel Weststrate, 40min, slides.
• CityJS 2020: MobX, from mutable to immutable, to observable data by Michel Weststrate, 30min.
• OpenSourceNorth: Practical React with MobX (ES5) by Matt Ruby, 42min.
• HolyJS 2019: MobX and the unique symbiosis of predictability and speed by Michel Weststrate, 59min.
• React Amsterdam 2016: State Management Is Easy by Michel Weststrate, 20min, slides.
• {🚀} React Live 2019: Reinventing MobX by Max Gallo, 27min.

And an all around MobX awesome list.

Credits

MobX is inspired by reactive programming principles as found in the spreadsheets. It is inspired by MVVM frameworks like MeteorJS tracker, knockout and Vue.js, but MobX brings Transparent Functional Reactive Programming to the next level and provides a standalone implementation. It implements TFRP in a glitch-free, synchronous, predictable and efficient manner.

A ton of credits goes to Mendix, for providing the flexibility and support to maintain MobX and the chance to proof the philosophy of MobX in a real, complex, performance critical applications.