ES6 Iterators

sample.js

function $range(...args) {
    let [start, stop, step] = args
    if (stop === undefined) {
        stop = start
        start = 0
    }

    let direction = start < stop ? 1 : -1
    let i = start
    step = step || (1 * direction)

    return {
        [Symbol.iterator]: () => ({
        	start,
            stop,
            step,
            next() {
            	if (direction > 0 ? i >= stop : i <= stop) {
                    return { done: true }
                } 

                let j = i
                i += step
                return {
                    done: false,
                    value: j
                }
            }
        })
    }
}

for (let i of $range(10)) {
    console.log("=", i)
}

for (let i of $range(10, 0)) {
    console.log("=", i)
}

for (let i of $range(10, 0, -2)) {
    console.log("=", i)
}