MobX is a simple, scalable and battle tested state management solution. This tutorial will teach you all the important concepts of MobX in ten minutes. MobX is a standalone library, but most people are using it with React and this tutorial focuses on that combination.

The core idea

State is the heart of each application and there is no quicker way to create buggy, unmanageable applications than by producing an inconsistent state or state that is out-of-sync with local variables that linger around. Hence many state management solutions try to restrict the ways in which you can modify state, for example by making state immutable. But this introduces new problems; data needs to be normalized, referential integrity can no longer be guaranteed and it becomes next to impossible to use powerful concepts like prototypes.


MobX makes state management simple again by addressing the root issue: it makes it impossible to produce an inconsistent state. The strategy to achieve that is simple: Make sure that everything that can be derived from the application state, will be derived. Automatically.

Conceptually MobX treats your application like a spreadsheet.

  • First of all, there is the application state. Graphs of objects, arrays, primitives, references that forms the model of your application. These values are the “data cells” of your application.
  • Secondly there are derivations. Basically, any value that can be computed automatically from the state of your application. These derivations, or computed values, can range from simple values, like the number of unfinished todos, to complex stuff like a visual HTML representation of your todos. In spreadsheet terms: these are the formulas and charts of your application.
  • Reactions are very similar to derivations. The main difference is these functions don’t produce a value. Instead, they run automatically to perform some task. Usually this is I/O related. They make sure that the DOM is updated or that network requests are made automatically at the right time.
  • Finally there are actions. Actions are all the things that alter the state. MobX will make sure that all changes to the application state caused by your actions are automatically processed by all derivations and reactions. Synchronously and glitch-free.


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 very simple: Anything that can be derived from the application state, should be derived. Automatically., which includes the UI, data serialization, server communication, etc.


React and MobX together are a powerful combination. React renders the application state by providing mechanisms to translate it into a tree of renderable components. MobX provides the mechanism to store and update the application state that React then uses.

Both React and MobX provide an optimal and unique solutions to common problems in application development. React provides mechanisms to optimally render UI by using a virtual DOM that reduces the number of costly DOM mutations. MobX provides mechanisms to optimally synchronize application state with your React components by using a reactive virtual dependency state graph that is only updated when strictly needed and is never stale.

Browser support

  • MobX >=5 runs on any browser with ES6 proxy support. It will throw an error on startup on older environments such as IE11, Node.js <6 or React Native Android on old JavaScriptCore how-to-upgrade.
  • MobX 4 runs on any ES5 browser and will be actively maintained. The MobX 4 and 5 api’s are the same and semantically can achieve the same, but MobX 4 has some limitations.

Tip: the main entry point of the MobX 5 package ships with ES5 code for backward compatibility with all build tools. But since MobX 5 runs only on modern browsers anyway, consider using the faster and smaller ES6 build: lib/mobx.es6.js. For example by setting up a Webpack alias: resolve: { alias: { mobx: __dirname + "/node_modules/mobx/lib/mobx.es6.js" }}