ECMAscript 6: watch changes to class properties

Question

Let's say I have a class defined as follows:

class MyClass {

    constructor (a) {
        this.a = a;     
    }

    _onPropertyChanged() {
        // do something
    }
}

Whenever the property "a" of an instance of MyClass changes, I want to trigger the _onPropertyChanged method on that instance. What is the best (most performant) way to achieve this using ECMAscript 6?

Answer 1

There's no 'best' way, and the actual approach always depends on the final goal.

In its simplistic (and performant enough) form it is:

class MyClass {

    constructor (a) {
      this.a = a;     
    }

    get a() {
      return this._a;
    }

    set a(val) {
      this._a = val;
      this._onPropertyChanged('a', val);
    }

    _onPropertyChanged(propName, val) {
        // do something
    }
}

Answer 2

This is a simple example of what you can do for this situation and for a single property.

class MyClass {

constructor (a) {
    this._a = a;
}

set a(value) {
    let hasChanged = (this._a !== value);
    this._a = value;
    //Assumes value is primitive. Customize for objects
    if(hasChanged) this._onPropertyChanged();

}

_onPropertyChanged() {
    // do something
}
}