Object.observe is dead. Long live MobX.observe

How does it work?

Beyond ‘observe’


  1. Adding a new property to an existing object is not detected automatically. Either declare the property upfront with an ‘undefined’ value, use ‘mobx.extendObservable’ to add the property, or create an observable ES6 like map using ‘mobx.map()’.
  2. Observable arrays aren’t actually arrays but objects instead. They behave just like normal arrays but external libraries might not properly recognize them. In such cases, just ‘.slice()’ the array before passing it to an external library.



Lead Developer @Mendix, JS, TS & React fanatic, dad (twice), creator of MobX, MX RestServices, nscript, mxgit. Created.

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