Generator 函数和for...of循环，实现斐波那契数列

function* fib () {
    let [prev, cur] = [0,1]
    for (;;) {
        yield cur
        [prev, cur] = [cur, cur+prev]
    }
}

for (let item of fib()) {
    if (item > 1000)  break;
        console.log(item)
}