iterable javascript

let range = {
    from: 1,
    to: 5
};
// 1. call to for..of initially calls this
range[Symbol.iterator] = function () {
    // ...it returns the iterator object:
    // 2. Onward, for..of works only with this iterator, asking it for next values
    return {
        current: this.from,
        last: this.to,

        // 3. next() is called on each iteration by the for..of loop
        next() {
            // 4. it should return the value as an object {done:.., value :...}
            if (this.current <= this.last) {
                return { done: false, value: this.current++ };
            } else {
                return { done: true };
            }
        }
    };
};
console.log(range); //Object { from: 1, to: 5, Symbol(Symbol.iterator): Symbol.iterator() }
console.log(range[Symbol.iterator]()); //Object { current: 1, last: 5, next: next() }
console.log(range[Symbol.iterator]().next()); //Object { done: false, value: 1 }
// now it works!
for (let num of range) {
    console.log(num); // 1, then 2, 3, 4, 5
}