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MobX is a state management library for JavaScript applications. It enables developers to manage the application state outside of UI frameworks in a reactive way that ensures that the state is consistent and predictable. MobX uses observable data structures and automatically tracks changes, updating the UI when necessary.
Observable State
Create observable state that can be tracked and updated. When the state changes, MobX will automatically propagate changes to any computed values or reactions that depend on the changed state.
import { observable } from 'mobx';
const appState = observable({
count: 0,
increment: function() {
this.count++;
},
decrement: function() {
this.count--;
}
});
Computed Values
Define computed values that will be re-evaluated when any observable data they depend on changes. Computed values are cached and only updated when necessary.
import { computed, makeObservable } from 'mobx';
class TodoList {
todos = [];
get unfinishedTodoCount() {
return this.todos.filter(todo => !todo.finished).length;
}
constructor() {
makeObservable(this, {
todos: observable,
unfinishedTodoCount: computed
});
}
}
Reactions
Reactions are a way to automatically run side effects when observable data changes. The autorun function is one type of reaction that runs immediately and then re-runs every time its dependencies change.
import { observable, autorun } from 'mobx';
const temperature = observable.box(20);
const reaction = autorun(() => {
console.log(`Temperature is: ${temperature.get()}C`);
});
temperature.set(25); // This will trigger the autorun and log the new temperature
Actions
Actions are functions that modify observables. They are the only way to modify state in MobX, and they can be bound to the class instance using the action.bound decorator.
import { observable, action } from 'mobx';
class Store {
@observable count = 0;
@action.bound increment() {
this.count++;
}
@action.bound decrement() {
this.count--;
}
}
Redux is a predictable state container for JavaScript apps. It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test. Unlike MobX, Redux uses a single immutable state tree and pure reducer functions to handle state changes.
Vuex is a state management pattern and library for Vue.js applications. It serves as a centralized store for all the components in an application, with rules ensuring that the state can only be mutated in a predictable fashion. Vuex is similar to Redux and differs from MobX in its strict emphasis on mutation tracking and less focus on reactive programming.
Immer is a tiny package that allows you to work with immutable state in a more convenient way. It uses a copy-on-write mechanism to ensure that the original state is not modified. While Immer is not a state management library like MobX, it can be used with state management libraries to simplify handling immutable data.
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+ per month):
🥉 Bronze sponsors ($500+ total contributions):
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:
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.
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.
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.
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).
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!
Created by Pavan Podila and Michel Weststrate.
And an all around MobX awesome list.
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.
FAQs
Simple, scalable state management.
The npm package mobx receives a total of 1,287,328 weekly downloads. As such, mobx popularity was classified as popular.
We found that mobx demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 6 open source maintainers collaborating on the project.
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