// instantiate
var a = {}
var b = {}

// set values
a.val = 10

// check values
console.log("A.val is:", a.val) //=> 10
console.log("B.val is:", b.val) //=> undefined

// bind values
Object.defineProperties(a, {
  val: {
	configurable: true, // can be changed or deleted
	enumerable: true,   // can be interated over
	get: ()=> this.val,
	set: (value)=> {
	    this.val = value
        b.val = value
    }
  }
})

// reset value
a.val = 20

// check values
console.log("A.val is:", a.val) // => 20
console.log("B.val is:", b.val) // => 20