proxy_set.js

"use strict";
let user = {
  name : "Jagathish",
  age : 23,
  mobile : 123123123,
  address : "221B Baker Stree, London"
};

let handler = {
  set(target, prop, val){
    if(prop in target){
      target[prop] = val;
      return true; // if the proprty is changed return true
    } else {
        return false; // if the proprty is not changed return false
    }
  }
};
user = new Proxy(user, handler);
user.age = 24;
console.log(user.age);//24
user.sex = "Male";
console.log(user.sex); //undefined