js实现sleep效果

/**
 *  睡眠函数
 *  @param numberMillis -- 要睡眠的毫秒数
 */
function sleep(numberMillis) {
    var now = new Date();
    var exitTime = now.getTime() + numberMillis;
    while (true) {
        now = new Date();
        if (now.getTime() > exitTime)
            return;
    }
}
for(var i = 1; i < 5 ; i++){
    console.info(i);
    sleep(3000);
}