dk-mobx-restore-state v3.2.14

Library for safe merging of MobX observables

!WARNING
It's fine if you use this library from NPM package with a static versioning in case you want it for some pet-project or to test it's capabilities.

But for production use it's strongly recommended to create a fork, because I do not write Changelogs and may break / add some functionality without notice.

Purpose

The purpose of this library is to safely restore state during SSR.

MobX 4 had a bug where newly added objects were not observable, like

const result = Object.assign(observable({ str: '123' }), { str: '321', obj: {} });

expect(isObservable(result.obj)).to.deep.eq(false); // BUG in MobX 4

Nowadays MobX 5 / 6 versions do not have this bug, we can use Object.assign. But when we speak about classes, the behavior remain inconsistent:

class Target {
  constructor() { makeAutoObservable(this); }
  str = '123';
}
    
const result = Object.assign(new Target(), { str: '321', obj: {} });

expect(isObservable(result.obj)).to.deep.eq(false); // BUG in all MobX versions

class Target {
  constructor() { makeAutoObservable(this); }
  str = '123';
  obj;
}
    
const result = Object.assign(new Target(), { str: '321', obj: {} });

expect(isObservable(result.obj)).to.deep.eq(false); // BUG in all MobX versions

class Target {
  constructor() { makeAutoObservable(this); }
  str = '123';
  obj = undefined;
}
    
const result = Object.assign(new Target(), { str: '321', obj: {} });

expect(isObservable(result.obj)).to.deep.eq(true); // No bug finally!

So, if you declare fore example user?: User inside your model and then SSR gives you a serialized object like user: { name: 'John' } it will not become observable if you use Object.assign(store, SSR_DATA).

This is very confusing and depends on transpilers (Babel, TSC, Esbuild, SWC) which all behave differently. So, this library makes everything consistent.

Usage

Install dk-mobx-restore-state and use it instead of Object.assign where needed. Everything will be observable (in MobX 4 or in class objects) in all the cases mentioned above.