js實現sleep

1.這種不是勻速, 寫到for循環中出現1,2,3.......456....的情況

function sleep(milliseconds) {
    var start = new Date().getTime();
    for (var i = 0; i < 1e7; i++) {
    if ((new Date().getTime() - start) > milliseconds){
            break;
        }
    }
}