Simple iterator

simple-iterator.js

const myObject = {
  a: 2,
  b: 3,
};

Object.defineProperty(myObject, Symbol.iterator, {
  enumerable: false,
  writable: false,
  configurable: true,
  value: function () {
    const obj = this;
    let idx = 0;
    const ks = Object.keys(obj);
    return {
      next: function () {
        return {
          value: obj[ks[idx++]],
          done: idx > ks.length,
        };
      },
    };
  },
});

// iterate `myObject` using iterator directly
const it = myObject[Symbol.iterator]();

console.log(it.next()); // { value:2, done:false }
console.log(it.next()); // { value:3, done:false }
console.log(it.next()); // { value:undefined, done:true }

// iterate `myObject` using `for..of`
for (const v of myObject) {
  console.log(v);
}
// 2
// 3