implementing range using iterator and generator

generator-iterator.js

class RangeIterable {
    constructor(start, end, step) {
        this.start = start;
        this.end = end;
        this.step = step;
        this.cnt = start;
    }

    [Symbol.iterator]() {
        return this;
    }

    next() {
        const done = this.cnt >= this.end;
        if (done) {
            return { done, value: undefined };
        }
        const value = this.cnt;
        this.cnt += this.step;
        return { done, value };
    }
}

function range(start, end, step = 1) {
    return new RangeIterable(start, end, step);
}

function* range(start, end, step = 1) {
    for (let i = start; i < end; i += step) {
        yield i;
    }
}

for (let v of range(1, 10, 3)) {
    console.log(v);
}