js实现sleep

1.这种不是匀速, 写到for循环中出现1,2,3.......456....的情况

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