observe() do not catch modifications done with set() method

[Strate]

observe(object, listener) do not catch modifications to existing props of object done with set. It only catches new property added. See jsfiddle: https://jsfiddle.net/4j6b3srp/

const a = mobx.extendObservable({}, {}, {}, {deep: false})

mobx.observe(a, console.log)

/*
logs {
  type: "add",
  object: {…},
  name: "prop1",
  newValue: "new prop"
}
as expected
*/
mobx.set(a, "prop1", "new prop") 

/*
expected to log {
  type: "update",
  object: {…},
  oldValue: "new prop",
  name: "prop1",
  newValue: "changed with set()"
}
but log do not happens
*/
mobx.set(a, "prop1", "changed with set()") 

/*
logs {
  type: "update",
  object: {…},
  oldValue: "changed with set()",
  name: "prop1",
  newValue: "changed with setter"
}
as expected
*/
a.prop1 = "changed with setter"

I think intercept is also affected

[quanganhtran]

I took a quick look at

mobx/src/api/object-api.ts

Lines 65 to 71 in dbe4c93

	const adm = ((obj as any) as IIsObservableObject).$mobx
	const existingObservable = adm.values[key]
	if (existingObservable) {
	existingObservable.set(value)
	} else {
	defineObservableProperty(obj, key, value, adm.defaultEnhancer)
	}

The first time when a new property is set, defineObservableProperty is called and will notify all listeners bound to obj, but subsequent calls to set get out the existingObservable which is an observable value with its own listeners.

Possible solution might be to set the new value through the parent observable object? In that case notification will go through for both the object and the value. Could make a PR if this sounds okay.

[mweststrate]

MR is merged and will be part of next release. Thanks @quanganhtran