JavaScript setInterval 和 setTimeout [英] JavaScript setInterval and setTimeout

问题描述

下一个代码每 1 秒显示一次日期，然后停止.

The next code display the date every 1 sec and then stops.

(function() {
    var i = setInterval(function() {
        console.log(new Date());
    }, 1000);
    console.log("Hi");

    setTimeout(function() {
        clearInterval(i);
    }, 3000);
    console.log("Hola");
})();

输出:

Hi
Hola
Wed Oct 24 2012 13:35:27 GMT+0200 (CEST)
Wed Oct 24 2012 13:35:28 GMT+0200 (CEST)
Wed Oct 24 2012 13:35:29 GMT+0200 (CEST)

但是不知道为什么先显示Hi和Hola.另外，为什么要执行 setTimeout ?不是假设 setInterval 每 1 秒执行一次而其他任何东西都不能执行吗?.(上面的代码是否按照编写的顺序运行?)谢谢.

But I don't know why Hi and Hola are displayed first. Also, why setTimeout is executed? It is not supposed that setInterval is executed every 1 sec and nothing else can be executed?. (Does the code above runs on the order in which it is written?) Thanks.

推荐答案

setTimeout 以及 setInterval 只注册函数(回调)，然后直接进入下一个命令.

setTimeout as well as setInterval only register functions (callbacks) but then go straight to the next command.

因此 Hi 和 Hola 在调用第一个回调之前打印.

Therefor Hi and Hola are printed before the first callbacks are called.

第一个回调将在 1 秒后是 setInterval，然后在 2 秒后再次回调.3 秒后 setTimeout 启动并清除 setInterval.

First callback will be that of setInterval after 1 sec, then again after 2 sec.. After 3 seconds setTimeout kicks in and clears setInterval.

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