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#efefef}.footer{padding-top:3rem}.footer-text{font-size:.8rem}</style></head><body class=""><div class="topbar"></div><div class="container"><a class="skip-link" href="#main-content">Skip to main content</a><nav class="nav"><ul class="navigation" id="navigation"><li class="navigation-item-emoji navigation-item-home"><a class="navigation-anchor" href="/'Front-end-Developer-Interview-Questions/'/" title="Home"><em>★</em><span>Front-end Developer Interview Questions</span></a></li><li class="navigation-item-emoji navigation-item-translations"><a class="navigation-anchor" href="/'Front-end-Developer-Interview-Questions/'/translations" title="Translations"><em>🌐</em><span>Translations</span></a></li><li class="navigation-item navigation-questions-label"><button class="navigation-toggle" id="navigation-toggle">Questions:</button></li><li class="navigation-item navigation-questions"><ul class="navigation navigation-questions-list"><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/general-questions/" title="General Questions">General</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/html-questions/" title="HTML Questions">HTML</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/css-questions/" title="CSS Questions">CSS</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/javascript-questions/" title="JavaScript Questions">JavaScript</a></li><li class="navigation-item"><a rel="external noreferrer noopener" target="_blank" class="navigation-anchor navigation-questions-anchor" href="https://scottaohara.github.io/accessibility_interview_questions/" title="Accessibility Questions (external link)">A11y</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/testing-questions/" title="Testing Questions">Testing</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/performance-questions/" title="Performance Questions">Performance</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/network-questions/" title="Network Questions">Network</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/coding-questions/" title="Coding Questions">Coding</a></li><li class="navigation-item"><a class="navigation-anchor navigation-questions-anchor" href="/'Front-end-Developer-Interview-Questions/'/questions/fun-questions/" title="Fun Questions">Fun</a></li></ul></li></ul></nav><main id="main-content" tabindex="-1"><header class="header"><h1 class="header-big-title">前端工作面试问题</h1></header><div class="content"><h1>前端工作面试问题</h1><p>本文包含了一些用于考查候选者的前端面试问题。不建议对单个候选者问及每个问题 (那需要好几个小时)。只要从列表里挑选一些，就能帮助你考查候选者是否具备所需要的技能。</p><p><strong>备注：</strong> 这些问题中很多都是开放性的，可以引发有趣的讨论。这比直接的答案更能体现此人的能力。</p><h2 id="%E7%9B%AE%E5%BD%95" tabindex="-1"><a class="header-anchor" href="#%E7%9B%AE%E5%BD%95"></a> <a name="toc">目录</a></h2><ol><li><a href="#general-questions">常见问题</a></li><li><a href="#html-questions">HTML 相关问题</a></li><li><a href="#css-questions">CSS 相关问题</a></li><li><a href="#js-questions">JS 相关问题</a></li><li><a href="#testing-questions">测试相关问题</a></li><li><a href="#performance-questions">效能相关问题</a></li><li><a href="#network-questions">网络相关问题</a></li><li><a href="#coding-questions">代码相关问题</a></li><li><a href="#fun-questions">趣味问题</a></li></ol><h2 id="%E5%8F%82%E4%B8%8E%E5%8D%8F%E4%BD%9C" tabindex="-1"><a class="header-anchor" href="#%E5%8F%82%E4%B8%8E%E5%8D%8F%E4%BD%9C"></a> 参与协作</h2><ol><li><a href="#contributors">贡献者</a></li><li><a href="https://github.com/h5bp/Front-end-Developer-Interview-Questions/blob/master/CONTRIBUTING.md">如何参与贡献</a></li><li><a href="https://github.com/h5bp/Front-end-Developer-Interview-Questions/blob/master/LICENSE.md">许可协议</a></li></ol><h4><a name="general-questions">常见问题：</a></h4><ul><li>你在昨天/本周学到了什么？</li><li>编写代码的哪些方面能够使你兴奋或感兴趣？</li><li>你最近遇到过什么技术挑战？你是如何解决的？</li><li>在制作一个网页应用或网站的过程中，你是如何考虑其 UI、安全性、高性能、SEO、可维护性以及技术因素的？</li><li>请谈谈你喜欢的开发环境。</li><li>你最熟悉哪一套版本控制系统？</li><li>你能描述当你制作一个网页的工作流程吗？</li><li>假若你有 5 个不同的样式文件 (stylesheets), 整合进网站的最好方式是?</li><li>你能描述渐进增强 (progressive enhancement) 和优雅降级 (graceful degradation) 之间的不同吗?</li><li>你如何对网站的文件和资源进行优化？</li><li>浏览器同一时间可以从一个域名下载多少资源？<ul><li>有什么例外吗？</li></ul></li><li>请说出三种减少页面加载时间的方法。(加载时间指感知的时间或者实际加载时间)</li><li>如果你参与到一个项目中，发现他们使用 Tab 来缩进代码，但是你喜欢空格，你会怎么做？</li><li>请写一个简单的幻灯效果页面。</li><li>如果今年你打算熟练掌握一项新技术，那会是什么？</li><li>请谈谈你对网页标准和标准制定机构重要性的理解。</li><li>什么是 FOUC (无样式内容闪烁)？你如何来避免 FOUC？</li><li>请解释什么是 ARIA 和屏幕阅读器 (screenreaders)，以及如何使网站实现无障碍访问 (accessible)。</li><li>请解释 CSS 动画和 JavaScript 动画的优缺点。</li><li>什么是跨域资源共享 (CORS)？它用于解决什么问题？</li></ul><h4><a name="html-questions">HTML 相关问题：</a></h4><ul><li><code>doctype</code>(文档类型) 的作用是什么？</li><li>浏览器标准模式 (standards mode) 、几乎标准模式（almost standards mode）和怪异模式 (quirks mode) 之间的区别是什么？</li><li>HTML 和 XHTML 有什么区别？</li><li>如果页面使用 ‘application/xhtml+xml’ 会有什么问题吗？</li><li>如果网页内容需要支持多语言，你会怎么做？</li><li>在设计和开发多语言网站时，有哪些问题你必须要考虑？</li><li>使用 <code>data-</code> 属性的好处是什么？</li><li>如果把 HTML5 看作做一个开放平台，那它的构建模块有哪些？</li><li>请描述 <code>cookies</code>、<code>sessionStorage</code> 和 <code>localStorage</code> 的区别。</li><li>请解释 <code><script></code>、<code><script async></code> 和 <code><script defer></code> 的区别。</li><li>为什么通常推荐将 CSS <code><link></code> 放置在 <code><head></head></code> 之间，而将 JS <code><script></code> 放置在 <code></body></code> 之前？你知道有哪些例外吗？</li><li>什么是渐进式渲染 (progressive rendering)？</li><li>你用过哪些不同的 HTML 模板语言？</li></ul><h4><a name="css-questions">CSS 相关问题：</a></h4><ul><li>CSS 中类 (classes) 和 ID 的区别。</li><li>请问 “resetting” 和 “normalizing” CSS 之间的区别？你会如何选择，为什么？</li><li>请解释浮动 (Floats) 及其工作原理。</li><li>描述<code>z-index</code>和叠加上下文是如何形成的。</li><li>请描述 BFC(Block Formatting Context) 及其如何工作。</li><li>列举不同的清除浮动的技巧，并指出它们各自适用的使用场景。</li><li>请解释 CSS sprites，以及你要如何在页面或网站中实现它。</li><li>你最喜欢的图片替换方法是什么，你如何选择使用。</li><li>你会如何解决特定浏览器的样式问题？</li><li>如何为有功能限制的浏览器提供网页？<ul><li>你会使用哪些技术和处理方法？</li></ul></li><li>有哪些的隐藏内容的方法 (如果同时还要保证屏幕阅读器可用呢)？</li><li>你用过栅格系统 (grid system) 吗？如果使用过，你最喜欢哪种？</li><li>你用过媒体查询，或针对移动端的布局/CSS 吗？</li><li>你熟悉 SVG 样式的书写吗？</li><li>如何优化网页的打印样式？</li><li>在书写高效 CSS 时会有哪些问题需要考虑？</li><li>使用 CSS 预处理器的优缺点有哪些？<ul><li>请描述你曾经使用过的 CSS 预处理器的优缺点。</li></ul></li><li>如果设计中使用了非标准的字体，你该如何去实现？</li><li>请解释浏览器是如何判断元素是否匹配某个 CSS 选择器？</li><li>请描述伪元素 (pseudo-elements) 及其用途。</li><li>请解释你对盒模型的理解，以及如何在 CSS 中告诉浏览器使用不同的盒模型来渲染你的布局。</li><li>请解释 <code>* { box-sizing: border-box; }</code> 的作用, 并且说明使用它有什么好处？</li><li>请罗列出你所知道的 display 属性的全部值</li><li>请解释 inline 和 inline-block 的区别？</li><li>请解释 relative、fixed、absolute 和 static 元素的区别</li><li>CSS 中字母 ‘C’ 的意思是叠层 (Cascading)。请问在确定样式的过程中优先级是如何决定的 (请举例)？如何有效使用此系统？</li><li>你在开发或生产环境中使用过哪些 CSS 框架？你觉得应该如何改善他们？</li><li>请问你有尝试过 CSS Flexbox 或者 Grid 标准规格吗？</li><li>为什么响应式设计 (responsive design) 和自适应设计 (adaptive design) 不同？</li><li>你有兼容 retina 屏幕的经历吗？如果有，在什么地方使用了何种技术？</li><li>请问为何要使用 <code>translate()</code> 而非 <em>absolute positioning</em>，或反之的理由？为什么？</li></ul><h4><a name="js-questions">JS 相关问题：</a></h4><ul><li>请解释事件代理 (event delegation)。</li><li>请解释 JavaScript 中 <code>this</code> 是如何工作的。</li><li>请解释原型继承 (prototypal inheritance) 的原理。</li><li>你怎么看 AMD vs. CommonJS？</li><li>请解释为什么接下来这段代码不是 IIFE (立即调用的函数表达式)：<code>function foo(){ }();</code>.<ul><li>要做哪些改动使它变成 IIFE?</li></ul></li><li>描述以下变量的区别：<code>null</code>，<code>undefined</code> 或 <code>undeclared</code>？<ul><li>该如何检测它们？</li></ul></li><li>什么是闭包 (closure)，如何使用它，为什么要使用它？</li><li>请举出一个匿名函数的典型用例？</li><li>你是如何组织自己的代码？是使用模块模式，还是使用经典继承的方法？</li><li>请指出 JavaScript 宿主对象 (host objects) 和原生对象 (native objects) 的区别？</li><li>请指出以下代码的区别：<code>function Person(){}</code>、<code>var person = Person()</code>、<code>var person = new Person()</code>？</li><li><code>.call</code> 和 <code>.apply</code> 的区别是什么？</li><li>请解释 <code>Function.prototype.bind</code>？</li><li>在什么时候你会使用 <code>document.write()</code>？</li><li>请指出浏览器特性检测，特性推断和浏览器 UA 字符串嗅探的区别？</li><li>请尽可能详尽的解释 Ajax 的工作原理。</li><li>使用 Ajax 都有哪些优劣？</li><li>请解释 JSONP 的工作原理，以及它为什么不是真正的 Ajax。</li><li>你使用过 JavaScript 模板系统吗？<ul><li>如有使用过，请谈谈你都使用过哪些库？</li></ul></li><li>请解释变量声明提升 (hoisting)。</li><li>请描述事件冒泡机制 (event bubbling)。</li><li>“attribute” 和 “property” 的区别是什么？</li><li>为什么扩展 JavaScript 内置对象不是好的做法？</li><li>请指出 document load 和 document DOMContentLoaded 两个事件的区别。</li><li><code>==</code> 和 <code>===</code> 有什么不同？</li><li>请解释 JavaScript 的同源策略 (same-origin policy)。</li><li>如何实现下列代码：</li></ul><pre class="language-javascript"><code class="language-javascript"><span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">,</span><span class="token number">5</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">duplicator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// [1,2,3,4,5,1,2,3,4,5]</span></code></pre><ul><li>什么是三元表达式 (Ternary expression)？“三元 (Ternary)” 表示什么意思？</li><li>什么是 <code>"use strict";</code> ? 使用它的好处和坏处分别是什么？</li><li>请实现一个遍历至 <code>100</code> 的 for loop 循环，在能被 <code>3</code> 整除时输出 <strong>“fizz”</strong>，在能被 <code>5</code> 整除时输出 <strong>“buzz”</strong>，在能同时被 <code>3</code> 和 <code>5</code> 整除时输出 <strong>“fizzbuzz”</strong>。</li><li>为何通常会认为保留网站现有的全局作用域 (global scope) 不去改变它，是较好的选择？</li><li>为何你会使用 <code>load</code> 之类的事件 (event)？此事件有缺点吗？你是否知道其他替代品，以及为何使用它们？</li><li>请解释什么是单页应用 (single page app), 以及如何使其对搜索引擎友好 (SEO-friendly)。</li><li>你使用过 Promises 及其 polyfills 吗? 请写出 Promise 的基本用法（ES6）。</li><li>使用 Promises 而非回调 (callbacks) 优缺点是什么？</li><li>使用一种可以编译成 JavaScript 的语言来写 JavaScript 代码有哪些优缺点？</li><li>你使用哪些工具和技术来调试 JavaScript 代码？</li><li>你会使用怎样的语言结构来遍历对象属性 (object properties) 和数组内容？</li><li>请解释可变 (mutable) 和不变 (immutable) 对象的区别。<ul><li>请举出 JavaScript 中一个不变性对象 (immutable object) 的例子？</li><li>不变性 (immutability) 有哪些优缺点？</li><li>如何用你自己的代码来实现不变性 (immutability)？</li></ul></li><li>请解释同步 (synchronous) 和异步 (asynchronous) 函数的区别。</li><li>什么是事件循环 (event loop)？<ul><li>请问调用栈 (call stack) 和任务队列 (task queue) 的区别是什么？</li></ul></li><li>解释 <code>function foo() {}</code> 与 <code>var foo = function() {}</code> 用法的区别</li></ul><h4><a name="testing-questions">测试相关问题：</a></h4><ul><li>对代码进行测试的有什么优缺点？</li><li>你会用什么工具测试你的代码功能？</li><li>单元测试与功能/集成测试的区别是什么？</li><li>代码风格 linting 工具的作用是什么？</li></ul><h4><a name="performance-questions">效能相关问题：</a></h4><ul><li>你会用什么工具来查找代码中的性能问题？</li><li>你会用什么方式来增强网站的页面滚动效能？</li><li>请解释 layout、painting 和 compositing 的区别。</li></ul><h4><a name="network-questions">网络相关问题：</a></h4><ul><li>为什么传统上利用多个域名来提供网站资源会更有效？</li><li>请尽可能完整得描述从输入 URL 到整个网页加载完毕及显示在屏幕上的整个流程。</li><li>Long-Polling、Websockets 和 Server-Sent Event 之间有什么区别？</li><li>请描述以下 request 和 response headers：<ul><li>Diff. between Expires, Date, Age and If-Modified-…</li><li>Do Not Track</li><li>Cache-Control</li><li>Transfer-Encoding</li><li>ETag</li><li>X-Frame-Options</li></ul></li><li>什么是 HTTP method？请罗列出你所知道的所有 HTTP method，并给出解释。</li><li>请解释 HTTP status 301 与 302 的区别？</li></ul><h4><a name="coding-questions">代码相关的问题：</a></h4><p><em>问题：<code>foo</code>的值是什么？</em></p><pre class="language-javascript"><code class="language-javascript"><span class="token keyword">var</span> foo <span class="token operator">=</span> <span class="token number">10</span> <span class="token operator">+</span> <span class="token string">'20'</span><span class="token punctuation">;</span></code></pre><p><em>问题：如何实现以下函数？</em></p><pre class="language-javascript"><code class="language-javascript"><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 7</span><br><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 7</span></code></pre><p><em>问题：下面的语句的返回值是什么？</em></p><pre class="language-javascript"><code class="language-javascript"><span class="token string">"i'm a lasagna hog"</span><span class="token punctuation">.</span><span class="token function">split</span><span class="token punctuation">(</span><span class="token string">""</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">reverse</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token string">""</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre><p><em>问题：<code>window.foo</code>的值是什么？</em></p><pre class="language-javascript"><code class="language-javascript"><span class="token punctuation">(</span> window<span class="token punctuation">.</span>foo <span class="token operator">||</span> <span class="token punctuation">(</span> window<span class="token punctuation">.</span>foo <span class="token operator">=</span> <span class="token string">"bar"</span> <span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre><p><em>问题：下面两个 alert 的结果是什么？</em></p><pre class="language-javascript"><code class="language-javascript"><span class="token keyword">var</span> foo <span class="token operator">=</span> <span class="token string">"Hello"</span><span class="token punctuation">;</span><br><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><br> <span class="token keyword">var</span> bar <span class="token operator">=</span> <span class="token string">" World"</span><span class="token punctuation">;</span><br> <span class="token function">alert</span><span class="token punctuation">(</span>foo <span class="token operator">+</span> bar<span class="token punctuation">)</span><span class="token punctuation">;</span><br><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><br><span class="token function">alert</span><span class="token punctuation">(</span>foo <span class="token operator">+</span> bar<span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre><p><em>问题：<code>foo.length</code>的值是什么？</em></p><pre class="language-javascript"><code class="language-javascript"><span class="token keyword">var</span> foo <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">;</span><br>foo<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span><br>foo<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre><p><em>问题：<code>foo.x</code>的值是什么？</em></p><pre class="language-javascript"><code class="language-javascript"><span class="token keyword">var</span> foo <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token literal-property property">n</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">}</span><span class="token punctuation">;</span><br><span class="token keyword">var</span> bar <span class="token operator">=</span> foo<span class="token punctuation">;</span><br>foo<span class="token punctuation">.</span>x <span class="token operator">=</span> foo <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token literal-property property">n</span><span class="token operator">:</span> <span class="token number">2</span><span class="token punctuation">}</span><span class="token punctuation">;</span></code></pre><p><em>问题：下面代码的输出是什么？</em></p><pre class="language-javascript"><code class="language-javascript">console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'one'</span><span class="token punctuation">)</span><span class="token punctuation">;</span><br><span class="token function">setTimeout</span><span class="token punctuation">(</span><span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><br> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'two'</span><span class="token punctuation">)</span><span class="token punctuation">;</span><br><span class="token punctuation">}</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span><br>console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'three'</span><span class="token punctuation">)</span><span class="token punctuation">;</span></code></pre><h4><a name="fun-questions">趣味问题：</a></h4><ul><li>你最近写过什么的很酷的项目吗？</li><li>在你使用的开发工具中，最喜欢哪些方面？</li><li>谁使你踏足了前端开发领域？</li><li>你有什么业余项目吗？是哪种类型的？</li><li>你最爱的 IE 特性是什么？</li><li>你对咖啡有没有什么喜好？</li></ul><h4><a name="contributors">贡献者：</a></h4><p>本文档始于 2009 年，是以下作者的合作成果：<a href="https://twitter.com/paul_irish">@paul_irish</a> <a href="https://twitter.com/bentruyman">@bentruyman</a> <a href="https://twitter.com/cowboy">@cowboy</a> <a href="https://twitter.com/ajpiano">@ajpiano</a> <a href="https://twitter.com/slexaxton">@SlexAxton</a> <a href="https://twitter.com/boazsender">@boazsender</a> <a href="https://twitter.com/miketaylr">@miketaylr</a> <a href="https://twitter.com/vladikoff">@vladikoff</a> <a href="https://twitter.com/gf3">@gf3</a> <a href="https://twitter.com/jon_neal">@jon_neal</a> <a href="https://twitter.com/sambreed">@sambreed</a> 和 <a href="https://twitter.com/iansym">@iansym</a>。</p><p>时至今日，文档已经融入超过 <a href="https://github.com/h5bp/Front-end-Developer-Interview-Questions/graphs/contributors">100 位开发者</a>的贡献。</p></div><div class="content-edit"><a rel="external noreferrer noopener" target="_blank" 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