深度解析JS事件驱动模型：如何理解浏览器中的异步回调和事件循环

@charset "UTF-8";
.markdown-body { line-height: 1.75; font-weight: 400; font-size: 15px; overflow-x: hidden; color: rgba(43, 43, 43, 1); font-family: -apple-system, system-ui, BlinkMacSystemFont, Helvetica Neue, PingFang SC, Hiragino Sans GB, Microsoft YaHei, Arial, sans-serif; background-image: linear-gradient(90deg, rgba(159, 219, 252, 0.15) 3%, rgba(0, 0, 0, 0) 0), linear-gradient(1turn, rgba(159, 219, 252, 0.15) 3%, rgba(0, 0, 0, 0) 0); background-size: 20px 20px; background-position: center }
.markdown-body h1, .markdown-body h2, .markdown-body h3, .markdown-body h4, .markdown-body h5, .markdown-body h6 { padding: 30px 0; margin-top: 35px; margin-bottom: 10px; color: rgba(77, 208, 225, 1) }
.markdown-body h1 { font-size: 30px; text-align: center; position: relative; width: max-content; margin: 0 auto }
.markdown-body h1:before { position: absolute; content: ""; z-index: -1; top: -20px; height: 100%; width: 100px; left: 0; right: 0; margin: 0 auto; background: url("data:image/png;base64,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") center / 64px 64px no-repeat; opacity: 0.84 }
.markdown-body h1:after { position: absolute; content: ""; width: 150%; left: -25%; height: 50%; bottom: 12px; border-radius: 50%; background: linear-gradient(rgba(0, 0, 0, 0) 80%, rgba(77, 208, 225, 0.8)); opacity: 0.6; animation: 6s linear infinite h1animate }
@keyframes h1Animate { 0% { background-position: right bottom } 50% { background-position: right } 100% { background-position: right bottom } }
.markdown-body h2 { display: block; border-bottom: 4px solid rgba(77, 208, 225, 1); position: relative; font-size: 24px; padding: 12px 32px; margin: 30px 0 }
.markdown-body h2:before { width: 24px; height: 24px; left: 0; top: 0; margin: auto; background-size: 24px 24px; background-image: url("data:image/png;base64,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") }
.markdown-body h2:after, .markdown-body h2:before { content: ""; display: block; position: absolute; bottom: 0 }
.markdown-body h2:after { right: 0; width: 400px; height: 10px; border-top-right-radius: 24px; background: linear-gradient(90deg, rgba(255, 255, 255, 1), rgba(77, 208, 225, 1)); max-width: 50vw }
.markdown-body h3 { margin: 30px 0; font-size: 18px; position: relative; padding: 4px 32px; width: max-content }
.markdown-body h3:before { border-bottom: 2px solid rgba(77, 208, 225, 1); width: 100%; content: ""; display: block; height: 28px; position: absolute; left: 0; top: 0; bottom: -2px; margin: auto; background-size: 28px 28px; background-image: url("data:image/png;base64,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"); background-repeat: no-repeat; animation: 2s infinite alternate h3animationbefore }
@keyframes h3AnimationBefore { 0% { width: 28px } 25% { width: 100% } 50% { width: 100% } 100% { width: 100% } }
.markdown-body h3:after { content: ""; display: block; width: 28px; height: 28px; position: absolute; border: 2px solid rgba(77, 208, 225, 1); border-radius: 50%; right: -15px; top: 0; bottom: 0; margin: auto; background-size: 28px 28px; background-image: url("data:image/png;base64,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"); animation: 2s infinite alternate h3animationafter }
@keyframes h3AnimationAfter { 0% { } 10% { } 50% { transform: rotate(-1turn) } 100% { transform: rotate(-1turn) } }
.markdown-body h4 { font-size: 16px }
.markdown-body h5 { font-size: 15px }
.markdown-body h6 { margin-top: 5px }
.markdown-body p { line-height: inherit; margin: 22px 0; letter-spacing: 2px; font-size: 14px; word-spacing: 2px }
.markdown-body img { max-width: 80%; border-radius: 6px; display: block; margin: 20px auto !important; object-fit: contain; box-shadow: 0 0 16px rgba(110, 110, 110, 0.45) }
.markdown-body figcaption { display: block; font-size: 13px; color: rgba(43, 43, 43, 1) }
.markdown-body figcaption:before { content: ""; background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgBAMAAACBVGfHAAAAGFBMVEVHcExAuPtAuPpAuPtAuPpAuPtAvPxAuPokzOX5AAAAB3RSTlMAkDLqNegkoiUM7wAAAGBJREFUKM9jYBhcgMkBTUDVBE1BeDGqEtXychNUBeXlKEqACsrLQxB8lnCQQClCiWt5OYoSiAIkJVAF5eVBqAqAShTAAs7l5ShKWMwRAmAlSArASpAVgJUkCqIAscESHwCVVjMBK9JnbQAAAABJRU5ErkJggg=="); display: inline-block; width: 18px; height: 18px; background-size: 18px; background-repeat: no-repeat; background-position: center; margin-right: 5px; margin-bottom: -5px }
.markdown-body hr { border-top: 1px solid rgba(77, 208, 225, 1); border-right: none; border-bottom: none; border-left: none; margin-top: 32px; margin-bottom: 32px }
.markdown-body del { color: rgba(77, 208, 225, 1) }
.markdown-body code { border-radius: 2px; overflow-x: auto; background-color: rgba(77, 208, 225, 0.08); color: rgba(38, 198, 218, 1); padding: 0.195em 0.4em }
.markdown-body pre { font-family: Menlo, Monaco, Consolas, Courier New, monospace; overflow: auto; position: relative; line-height: 1.75; box-shadow: 0 0 8px rgba(110, 110, 110, 0.45); border-radius: 4px; margin: 16px }
.markdown-body pre:before { content: ""; display: block; height: 30px; width: 100%; margin-bottom: -7px; background: url("data:image/png;base64,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") 10px 10px / 40px no-repeat }
.markdown-body pre>code { font-size: 12px; padding: 15px 12px; margin: 0; word-break: normal; display: block; overflow-x: auto; color: rgba(51, 51, 51, 1); background: rgba(248, 248, 248, 1) }
.markdown-body a { color: rgba(77, 208, 225, 1); border-bottom: 1px solid rgba(77, 208, 225, 1); font-weight: 400; text-decoration: none; margin: 0 4px }
.markdown-body a:active, .markdown-body a:hover { background-color: rgba(77, 208, 225, 0.1) }
.markdown-body strong { color: rgba(38, 198, 218, 1) }
.markdown-body strong:before { content: "「" }
.markdown-body strong:after { content: "」" }
.markdown-body em { font-style: normal; color: rgba(77, 208, 225, 1); font-weight: 700 }
.markdown-body table { display: inline-block !important; font-size: 12px; width: auto; max-width: 100%; overflow: auto; border: 1px solid rgba(246, 246, 246, 1) }
.markdown-body thead { background: rgba(246, 246, 246, 1); color: rgba(0, 0, 0, 1); text-align: left }
.markdown-body tr:nth-child(2n) { background-color: rgba(77, 208, 225, 0.05) }
.markdown-body td, .markdown-body th { padding: 12px 7px; line-height: 24px }
.markdown-body td { min-width: 120px }
.markdown-body blockquote { margin: 2em 0; padding: 24px 32px; border-left: 4px solid rgba(38, 198, 218, 1); background: rgba(77, 208, 225, 0.15); position: relative }
.markdown-body blockquote:before { content: "❝"; top: 8px; left: 8px; color: rgba(77, 208, 225, 1); font-size: 30px; line-height: 1; font-weight: 700; position: absolute; opacity: 0.7 }
.markdown-body blockquote:after { content: "❞"; font-size: 30px; position: absolute; right: 8px; bottom: 0; color: rgba(77, 208, 225, 1); opacity: 0.7 }
.markdown-body blockquote p { color: rgba(89, 89, 89, 1); line-height: 2 }
.markdown-body ol, .markdown-body ul { color: rgba(89, 89, 89, 1); padding-left: 28px }
.markdown-body ol li, .markdown-body ul li { margin-bottom: 0; list-style: inherit }
.markdown-body ol li .task-list-item, .markdown-body ul li .task-list-item { list-style: none }
.markdown-body ol li .task-list-item ol, .markdown-body ol li .task-list-item ul, .markdown-body ul li .task-list-item ol, .markdown-body ul li .task-list-item ul { margin-top: 0 }
.markdown-body ol ol, .markdown-body ol ul, .markdown-body ul ol, .markdown-body ul ul { margin-top: 3px }
.markdown-body ol li { padding-left: 6px }
@media (max-width: 720px) { .markdown-body h1 { font-size: 24px } .markdown-body h2 { font-size: 20px } .markdown-body h3 { font-size: 18px } }.markdown-body pre, .markdown-body pre>code.hljs { background: rgba(255, 255, 255, 1); color: rgba(0, 0, 0, 1) }
.hljs-comment, .hljs-quote, .hljs-variable { color: rgba(0, 128, 0, 1) }
.hljs-built_in, .hljs-keyword, .hljs-name, .hljs-selector-tag, .hljs-tag { color: rgba(0, 0, 255, 1) }
.hljs-addition, .hljs-attribute, .hljs-literal, .hljs-section, .hljs-string, .hljs-template-tag, .hljs-template-variable, .hljs-title, .hljs-type { color: rgba(163, 21, 21, 1) }
.hljs-deletion, .hljs-meta, .hljs-selector-attr, .hljs-selector-pseudo { color: rgba(43, 145, 175, 1) }
.hljs-doctag { color: rgba(128, 128, 128, 1) }
.hljs-attr { color: rgba(255, 0, 0, 1) }
.hljs-bullet, .hljs-link, .hljs-symbol { color: rgba(0, 176, 232, 1) }
.hljs-emphasis { font-style: italic }
.hljs-strong { font-weight: 700 }

日常刷JS面试题，难免会遇到这么一道：请简述JS的事件驱动模型。各位小伙伴是否也曾经有过这样的经历，对着这道题，一脸懵逼，一脸蒙圈。今天，掌门人就来给大家普及一下 JS 事件驱动模型的相关知识。

JS异步编程的背景：从回调地狱到Promise和async/await

在了解事件驱动模型之前，我们先回顾一下JS异步编程的历史。

记得刚开始写JS的时候，还没有现在流行的Promise和async/await，那时候我们可能还在回调地狱里挣扎。比如，要实现服务端的请求数据一般需要这样写：

getDataFromServer(params, function(err, result1){

  if (!err) {

    getNextResult(result1, function(err, result2) {

      if (!err) {

        getFinalResult(result2, function(err, result3) {

          if (!err) {

            // Do something with the result

          } else {

            console.log(err);

          }

        }

      } else {

        console.log(err);

      }

    });

  } else {

      console.log(err);

  }

});

这样的代码对于我们来说，一股绝望，如果嵌套多了，直接影响开发者的心情。但随着时间的推移，Promise和async/await逐渐逐渐变得越来越流行，如今已成为JS异步编程的标配。

用Promise和async/await实现上面代码的异步请求，大家一定更为熟悉，更为好看：

async function getDataFromServer(params) {

  try {

    const result1 = await fetch(url1);

    const result2 = await fetch(url2 + result1.id);

    const finalResult = await fetch(url3 + result2.id);

    // Do something with finalResult

  } catch (err) {

    console.log(err);

  }

}

异步编程变得更加方便了，但是背后却有什么本质的变化吗？实质上，JS的异步编程背后采用了事件驱动模型。

什么是JS事件驱动模型：理解事件循环、宏任务与微任务

事件驱动模型是什么？简单说来，是当特定事件发生时，某个函数或代码块会被触发和执行的一种编程方式。

JS事件驱动模型的核心是事件循环。所谓的事件循环就是一个不断循环的过程，JS引擎会检查宏队列和微队列里的任务有没有被处理完，如果宏队列和微队列均为空，则JS引擎会一直休眠，等待宏队列和微队列中被新加入的任务唤醒。其中，宏任务存放在宏任务队列中，常见的宏任务有setTimeout、setInterval、setImmediate和I/O操作等。而微任务则处于微任务队列中，常见的微任务有Promise.then、process.nextTick和object.observe，主要用于对象数据的监听。

console.log('script start');

setTimeout(function() {

  console.log('setTimeout');

}, 0);

Promise.resolve().then(function() {

  console.log('promise1');

}).then(function() {

  console.log('promise2');

});

console.log('script end');

运行上述代码，你会发现输出顺序是这样的：

script start

script end

promise1

promise2

setTimeout

我们来看一下这段代码的执行过程：

执行第一行代码，输出 "script start"。
设置一个0毫秒后执行的定时器，这个定时器是一个宏任务，被放到宏任务队列中。
解析Promise.resolve()语句，并将其添加到微任务队列中。因为微任务队列是在当前任务完成后立即执行的，所以接下来会立即执行微任务。
执行第7行代码，输出 "script end"。
当前任务同步代码执行完成，开始执行微任务。
执行第10行代码，输出 "promise1"，继续执行第11行代码，输出 "promise2"。
微任务队列为空，开始执行宏任务队列中的任务。
执行定时器回调函数，输出 "setTimeout"。

可以看到，微任务的执行优先于宏任务，而不同类型的任务又是按照队列的顺序依次执行的。了解这些背后的机制，会帮助我们更好地理解事件驱动模型在JS中的应用。

浏览器中的事件机制：从事件触发到事件处理的整个流程

在浏览器中，事件是如何被触发和处理的呢？下面是整个流程的简述：

用户在浏览器中触发一个事件，比如点击鼠标、按下键盘等。
事件被封装成Event对象。
Event对象被放入宏任务队列中，等待JS引擎执行。
当宏任务队列中的事件被执行时，JS引擎会把这个Event对象拿出来，并调用该事件对应的监听器或回调函数。
监听器或回调函数执行完成后，如果有相关的异步请求，JS引擎会把它们放入微任务队列中，等待当前宏任务执行完成后执行。

document.addEventListener('click', function(event) {

  console.log('You clicked the button');

});

在上述代码中，当用户点击页面中的某个元素时，就会触发click事件并被封装为Event对象，然后被添加到宏任务队列中等待执行。当JS引擎执行到这个宏任务时，会调用监听器函数并输出 "You clicked the button"。

常见事件类型的处理方式：鼠标/键盘事件、网络请求、DOM操作等

在浏览器中，事件类型很多，处理方式也各不相同。常见的事件类型包括鼠标/键盘事件、页面加载事件、网络请求事件、DOM操作等。下面是一些常见事件类型和处理方式的示例。

鼠标/键盘事件

document.addEventListener('mousemove', function(event) {

  console.log('Mouse position:', event.clientX, event.clientY);

});

document.addEventListener('keydown', function(event) {

  console.log('Key pressed:', event.keyCode);

});

当用户移动鼠标时，mousemove事件会被触发并产生一个Event对象，其中clientX和clientY属性表示鼠标的坐标位置。当用户按下键盘时，keydown事件也会产生一个Event对象，其中keyCode表示按下的键位。

网络请求事件

const req = new XMLHttpRequest();

req.open('GET', 'https://example.com/data');

req.addEventListener('load', function(event) {

  console.log('Data loaded:', req.responseText);

});

req.send();

使用XMLHttpRequest发送HTTP请求，当服务器返回响应时，load事件将被触发并产生一个Event对象，其中可以通过responseText属性获取服务器响应的数据。

DOM操作

const btn = document.getElementById('my-button');

btn.addEventListener('click', function(event) {

  event.preventDefault();

  console.log('Button clicked');

  // do something else

});

当用户点击按钮时，click事件会被触发并产生一个Event对象，其中preventDefault方法可以阻止默认行为，比如链接跳转等。

JS事件驱动模型的优化和性能问题：如何避免长任务影响用户体验？

在JS事件驱动模型的应用中，有一些常见的问题需要注意。其中一个重要的问题就是长任务的执行可能会导致UI线程阻塞，造成用户体验的不良影响。为了避免这种情况，我们需要优化代码，让长任务异步执行，并通过一些非阻塞的方式来处理。

代码示例：

const btn = document.getElementById('my-button');

btn.addEventListener('click', function(event) {

  console.log('Button clicked');

  setTimeout(function() {

    console.log('Long task started');

    // do something that takes a long time

    console.log('Long task finished');

  }, 0);

});

在上述代码中，当用户点击按钮时，会产生一个宏任务，其中的长任务被封装在一个定时器函数中并异步执行，从而不会阻塞UI线程的执行。

其他常见问题和应用场景：事件委托、事件冒泡、代码调试等

除了上述问题外，JS事件驱动模型还涉及到诸如事件委托、事件冒泡、代码调试等问题。下面我们来简要介绍这些问题和应用场景。

事件委托

事件委托指的是将事件绑定在父节点上，从而将事件的处理交给子节点。在大量的DOM节点绑定事件处理程序时，事件委托可以提高性能，避免内存泄漏等问题。

<ul id="my-list">

  <li>Item 1</li>

  <li>Item 2</li>

  <li>Item 3</li>

  <li>Item 4</li>

</ul>

// 绑定事件委托

const list = document.getElementById('my-list');

list.addEventListener('click', function(event) {

  const target = event.target;

  if (target.tagName === 'LI') {

    console.log('Clicked item:', target.textContent);

  }

});

在上述代码中，我们将点击事件绑定在ul元素上，而不是每个li元素上，从而减少了事件处理程序的数量和内存使用。

事件冒泡

事件冒泡指的是当某个元素触发了事件时，它的父元素也会触发该事件。

<div id="parent">

  <div id="child"></div>

</div>

// 绑定事件冒泡

const parent = document.getElementById('parent');

parent.addEventListener('click', function(event) {

  console.log('Parent clicked:', event.target.id);

});

const child = document.getElementById('child');

child.addEventListener('click', function(event) {

  console.log('Child clicked:', event.target.id);

});

在上述代码中，当点击child元素时，parent元素会触发点击事件，由于事件冒泡的机制，父元素和子元素的事件处理程序均会被执行。

代码调试

JS事件驱动模型中涉及到的事件和任务可能是异步的，我们需要使用适当的调试技术来调试代码，以便更好地理解事件驱动模型的实现和调试代码。

结论和展望：JS事件驱动模型的未来发展趋势

在未来，JS事件驱动模型可能会更加智能化，一些新的API和机制也将会出现，以便更好地满足业务需求和提高开发效率。

此外，技术不断更新，在了解JS事件驱动模型的基础上，我们还需要不断学习新的技术知识，不断探索和实践，才能不断提升自己的技能水平。

当然，在使用JS事件驱动模型时还需要注意效率和可维护性等问题，不断优化代码，提高性能和可读性，从而更好地应对各种场景的需求。

最后，我希望通过这篇文章，能够帮助大家更好地理解JS事件驱动模型的基本概念、应用场景和相关技巧，从而更好地编写和优化JavaScript代码。