Dependent javascript object properties [duplicate]

Question

How can I do something like this in javascript?

obj = {
    prop1 = 0;
    prop2 = 0;
    prop3 = prop1 + prop2;
}

So when obj.prop1 is updated so will obj.prop3 automatically.

Answer 1

Try to make prop3 getter/setter, see example

var obj = {
    prop1: 1,
    prop2: 4,
    get prop3() {
      return this.prop1 + this.prop2; 
    }
};

console.log(obj.prop3);
obj.prop1 = 6;
console.log(obj.prop3);