Introduction to MobX

a simple state management solution.


State Management......sound familiar?

a functional programming approach

three core principles:

1. store acts as a single source of truth

2. state is read-only and can only be changed by emitting an action

3. changes to state are made by pure functions - reducers





an object-oriented approach

key concepts:

1. actions - primary means to modify the state. They take sources of change like user events to modify the observable state.

2. observable state - any value that can be mutated.

3. computed values - derived automatically when relevant data (observable values) are modified.

4. reactions - side effects that display changes to the UI or help with logging to the console.






redux state lifecycle, a quick look

Visualizing MobX: 'it's like a spreadsheet!' 

Let's open up your Microsoft Excel or LibreOffice Calc

Ex. Spreadsheet

Observable values: all data cells that have values


Computed values: formulas and charts that can be derived from the data cells and other formulas


Reaction: drawing the output of a data cell or a formula of the screen


Action: changing a data cell or formula


  • the key first step to using MobX is to set your state and mark it as observable
  • this is signifying that these are values that can change over time, and that the values derived from these values must update accordingly


  • computed values are automatically derived from the state -- if any value that affects them changes they change with it
  • everything is synchronous - they update immediately (think of the spreadsheet formula)

@ @ @ @ @ @ @

what's a function decorator, anyway?

ES6 syntax for calling higher-order functions

a function that extends the behavior of a wrapped function but does not explicitly modify it.

with decorators

without decorators

Mobx Flow


Events invoke actions.

Actions are the only

thing that modify state

and may have other

side effects

@action onClick = () => {

    this.props.todo.done = true;



State is observable and minimally

defined. Should not contain

redundant or derivable data. Can

be a graph, contain classes, arrays, refs, etc.

@observable todos = [{

    title: "learn Mobx",

    done: false


Computed values

Computed values are values that

can be derived from the state

using a pure function.  Will be

updated automatically by Mobx

and optimized away if not use.

@computed get completedTodos() {

    return this.todos.filter(

        todo => todo.done




Reactions are like computed

values and react to state

changes.  But they produce a

side effect instead of a value,

like updating the UI.

const Todos = observer({ todos }) =>

    <ul> => <TodoView ... />



let's put it all together

the @observer


incredibly manual

  • to update state: explicitly dispatch actions and subscribe to the store. The manual definition of middleware and reducers gives you a lot of control.


  • application is predictable, testable and easy to reason about.


  • lot's of boilerplate, you have to write everything yourself.





incredibly magical

  • to update state: describe observable values that can be mutated and in turn mutate other values. Action dispatching and subscribing is automatic.


  • application is still predictable but perhaps more difficult to test/debug.


  • easier learning curve and significantly less code to write!



key differences

What is MobX

By Devlin Duldulao

What is MobX

Introduction to MobX: A Simple State Management Solution

  • 561