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<!DOCTYPE html>
<html class="theme-next pisces use-motion" lang="zh-Hans">
<head>
<meta charset="UTF-8"/>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"/>
<meta name="theme-color" content="#222">
<meta http-equiv="Cache-Control" content="no-transform" />
<meta http-equiv="Cache-Control" content="no-siteapp" />
<link href="/lib/fancybox/source/jquery.fancybox.css?v=2.1.5" rel="stylesheet" type="text/css" />
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<link href="/css/main.css?v=5.1.2" rel="stylesheet" type="text/css" />
<meta name="keywords" content="Hexo, NexT" />
<link rel="shortcut icon" type="image/x-icon" href="/favicon.ico?v=5.1.2" />
<meta name="description" content="加油！">
<meta property="og:type" content="website">
<meta property="og:title" content="liaoyf的博客">
<meta property="og:url" content="https://liaoyongfu.github.io/index.html">
<meta property="og:site_name" content="liaoyf的博客">
<meta property="og:description" content="加油！">
<meta property="og:locale" content="zh-Hans">
<meta name="twitter:card" content="summary">
<meta name="twitter:title" content="liaoyf的博客">
<meta name="twitter:description" content="加油！">
<script type="text/javascript" id="hexo.configurations">
var NexT = window.NexT || {};
var CONFIG = {
root: '/',
scheme: 'Pisces',
sidebar: {"position":"left","display":"post","offset":12,"offset_float":12,"b2t":false,"scrollpercent":false,"onmobile":false},
fancybox: true,
tabs: true,
motion: true,
duoshuo: {
userId: '0',
author: '博主'
},
algolia: {
applicationID: '',
apiKey: '',
indexName: '',
hits: {"per_page":10},
labels: {"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}
}
};
</script>
<link rel="canonical" href="https://liaoyongfu.github.io/"/>
<title>liaoyf的博客</title>
<script type="text/javascript">
var _hmt = _hmt || [];
(function() {
var hm = document.createElement("script");
hm.src = "https://hm.baidu.com/hm.js?9de8fd632ad583c841a2a4fa8c3f5bc4";
var s = document.getElementsByTagName("script")[0];
s.parentNode.insertBefore(hm, s);
})();
</script>
</head>
<body itemscope itemtype="http://schema.org/WebPage" lang="zh-Hans">
<div class="container sidebar-position-left
page-home
">
<div class="headband"></div>
<header id="header" class="header" itemscope itemtype="http://schema.org/WPHeader">
<div class="header-inner"><div class="site-brand-wrapper">
<div class="site-meta ">
<div class="custom-logo-site-title">
<a href="/" class="brand" rel="start">
<span class="logo-line-before"><i></i></span>
<span class="site-title">liaoyf的博客</span>
<span class="logo-line-after"><i></i></span>
</a>
</div>
<p class="site-subtitle">一分耕耘一分收获</p>
</div>
<div class="site-nav-toggle">
<button>
<span class="btn-bar"></span>
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</button>
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</div>
<nav class="site-nav">
<ul id="menu" class="menu">
<li class="menu-item menu-item-home">
<a href="/" rel="section">
<i class="menu-item-icon fa fa-fw fa-home"></i> <br />
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</a>
</li>
<li class="menu-item menu-item-tags">
<a href="/tags/" rel="section">
<i class="menu-item-icon fa fa-fw fa-tags"></i> <br />
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</a>
</li>
<li class="menu-item menu-item-archives">
<a href="/archives/" rel="section">
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</span>
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<input autocomplete="off"
placeholder="搜索..." spellcheck="false"
type="text" id="local-search-input">
</div>
</div>
<div id="local-search-result"></div>
</div>
</div>
</nav>
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<main id="main" class="main">
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<article class="post post-type-normal" itemscope itemtype="http://schema.org/Article">
<div class="post-block">
<link itemprop="mainEntityOfPage" href="https://liaoyongfu.github.io/2018/12/13/css/CSSDOM简介/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="name" content="liaoyf">
<meta itemprop="description" content="">
<meta itemprop="image" content="/images/avatar.jpg">
</span>
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<meta itemprop="name" content="liaoyf的博客">
</span>
<header class="post-header">
<h1 class="post-title" itemprop="name headline">
<a class="post-title-link" href="/2018/12/13/css/CSSDOM简介/" itemprop="url">CSSDOM简介</a></h1>
<div class="post-meta">
<span class="post-time">
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<span class="post-meta-item-text">发表于</span>
<time title="创建于" itemprop="dateCreated datePublished" datetime="2018-12-13T17:39:57+08:00">
2018-12-13
</time>
</span>
<span id="/2018/12/13/css/CSSDOM简介/" class="leancloud_visitors" data-flag-title="CSSDOM简介">
<span class="post-meta-divider">|</span>
<span class="post-meta-item-icon">
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</span>
<span class="post-meta-item-text">阅读次数 </span>
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<div class="post-body" itemprop="articleBody">
<h2 id="什么是CSSOM"><a href="#什么是CSSOM" class="headerlink" title="什么是CSSOM"></a>什么是CSSOM</h2><blockquote>
<p>CSS对象模型是一组允许从JavaScript处理CSS的API。它很像DOM，但对于CSS而不是HTML。它允许用户动态地读取和修改CSS样式。</p>
</blockquote>
<h2 id="通过element-style获取和设置内联样式"><a href="#通过element-style获取和设置内联样式" class="headerlink" title="通过element.style获取和设置内联样式"></a>通过element.style获取和设置内联样式</h2><p>使用JavaScript操作或访问CSS属性和值的最基本方法是通过元素的<code>style</code>属性进行操作：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">document.body.style.background = 'lightblue';</span><br><span class="line">document.body.style.width = '888px';</span><br><span class="line">document.body.style.cssFloat = 'left';</span><br></pre></td></tr></table></figure>
<p>这是使用JavaScript操作或获取CSS属性和值的简单方法。但是style以这种方式使用属性需要注意：<strong><em>这只适用于元素的内联样式</em></strong>。</p>
<p>如果元素没有定义内联样式，即时有一个外部样式文件，获取不存在的样式属性时将得不到任何东西：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">console.log(document.body.cssFloat) // ""</span><br></pre></td></tr></table></figure>
<p>这显然有一些显着的局限性，所以让我们看一些使用JavaScript阅读和操作样式的更有用的技术。</p>
<h2 id="获取计算样式"><a href="#获取计算样式" class="headerlink" title="获取计算样式"></a>获取计算样式</h2><p>可以使用以下<code>window.getComputedStyle()</code>方法读取元素上任何CSS属性的计算CSS值：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">widnow.getComputedStyle(document.body).background</span><br><span class="line">// "rgba(0, 0, 0, 0) none repeat scroll 0% 0% / auto padding-box border-box"</span><br><span class="line">getComputedStyle(document.body).width</span><br><span class="line">// "134px"</span><br></pre></td></tr></table></figure>
<p>计算属性将会得到最终的样式结果，包括浏览器默认的样式，这可能会得到太多东西了，(⊙o⊙)…！</p>
<p>有几种不同的方法可以使用<code>window.getComputedStyle()</code>：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">// dot notation, same as above</span><br><span class="line">window.getComputedStyle(el).backgroundColor;</span><br><span class="line"></span><br><span class="line">// square bracket notation</span><br><span class="line">window.getComputedStyle(el)['background-color'];</span><br><span class="line"></span><br><span class="line">// using getPropertyValue()</span><br><span class="line">window.getComputedStyle(el).getPropertyValue('background-color');</span><br></pre></td></tr></table></figure>
<h2 id="获取伪元素的计算样式"><a href="#获取伪元素的计算样式" class="headerlink" title="获取伪元素的计算样式"></a>获取伪元素的计算样式</h2><p>一个鲜为人知的小问题<code>window.getComputedStyle()</code>是，它允许您检索伪元素的样式信息。你会经常看到这样的<code>window.getComputedStyle()</code>声明：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">window.getComputedStyle(document.body, ":before").width;</span><br></pre></td></tr></table></figure>
<p>第二个可选参数允许我指定我正在访问伪元素的计算CSS。</p>
<h2 id="CSSStyleDeclaration"><a href="#CSSStyleDeclaration" class="headerlink" title="CSSStyleDeclaration"></a>CSSStyleDeclaration</h2><p>不管是通过<code>style</code>还是<code>window.getComputedStyle</code>，它返回的都是<code>CSSStyleDeclaration</code>对象，后者是只读的。</p>
<h2 id="setProperty-getPropertyValue-和-item"><a href="#setProperty-getPropertyValue-和-item" class="headerlink" title="setProperty(), getPropertyValue() 和 item()"></a>setProperty(), getPropertyValue() 和 item()</h2><p>考虑如下代码：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">let box = document.querySelector('.box');</span><br><span class="line"></span><br><span class="line">box.style.setProperty('color', 'orange');</span><br><span class="line">box.style.setProperty('font-family', 'Georgia, serif');</span><br><span class="line">op.innerHTML = box.style.getPropertyValue('color');</span><br><span class="line">op2.innerHTML = `${box.style.item(0)}, ${box.style.item(1)}`;</span><br></pre></td></tr></table></figure>
<ul>
<li><p><code>setProperty(css属性名，css属性值)</code></p>
</li>
<li><p><code>getPropertyValue(css属性名)</code></p>
</li>
<li><p><code>item(index)</code>：上图<code>item(0)</code>为<code>color</code>、<code>item(1)</code>为<code>font-family</code>，<code>item(2)</code>如果没有的话返回””</p>
</li>
</ul>
<h2 id="removeProperty"><a href="#removeProperty" class="headerlink" title="removeProperty()"></a>removeProperty()</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">box.style.setProperty('font-size', '1.5em');</span><br><span class="line">box.style.item(0) // "font-size"</span><br><span class="line"></span><br><span class="line">document.body.style.removeProperty('font-size');</span><br><span class="line">document.body.style.item(0); // ""</span><br></pre></td></tr></table></figure>
<h2 id="获取和设置属性的优先级"><a href="#获取和设置属性的优先级" class="headerlink" title="获取和设置属性的优先级"></a>获取和设置属性的优先级</h2><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">box.style.setProperty('font-family', 'Georgia, serif', 'important');</span><br><span class="line">box.style.setProperty('font-size', '1.5em');</span><br><span class="line"></span><br><span class="line">box.style.getPropertyPriority('font-family'); // important</span><br><span class="line">op2.innerHTML = box.style.getPropertyPriority('font-size'); // ""</span><br></pre></td></tr></table></figure>
<p>当<code>setProperty</code>增加第三个参数<code>important</code>时，<code>font-family</code>将会有<code>!important</code>权重。</p>
<p>我要强调的是，这些方法可以与已经直接放在HTML元素style属性上的任何内联样式一起使用。所以，如果我有以下HTML：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><div class="box" style="border: solid 1px red !important;"></span><br></pre></td></tr></table></figure>
<p>其他子属性也将会有<code>!important</code>权重。</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">// These all return "important"</span><br><span class="line">box.style.getPropertyPriority('border'));</span><br><span class="line">box.style.getPropertyPriority('border-top-width'));</span><br><span class="line">box.style.getPropertyPriority('border-bottom-width'));</span><br><span class="line">box.style.getPropertyPriority('border-color'));</span><br><span class="line">box.style.getPropertyPriority('border-style'));</span><br></pre></td></tr></table></figure>
<h2 id="CSSStyleSheet接口"><a href="#CSSStyleSheet接口" class="headerlink" title="CSSStyleSheet接口"></a>CSSStyleSheet接口</h2><p>从样式表访问信息的最简单方法是使用<code>document</code>开放的<code>styleSheets</code>属性，例如，下面的行使用该length属性来查看当前页面具有多少样式表：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">document.styleSheets.length; // 1</span><br></pre></td></tr></table></figure>
<p>我可以使用从零开始的索引来引用任何文档的样式表：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">document.styleSheets[0];</span><br></pre></td></tr></table></figure>
<p>它将返回<code>CSSStyleSheet</code>对象，里面最有用的是<code>cssRules</code>属性，此属性提供该样式表中包含的所有CSS规则（包括声明块，规则，媒体规则等）的列表。在下面的部分，我们将详细介绍该API的操作。</p>
<blockquote>
<p>cssRules（CSSRuleList） -> (CSSStyleRule) -> type, cssText, selectorText, style(CSSStyleDeclaration),…</p>
</blockquote>
<h2 id="使用样式表对象"><a href="#使用样式表对象" class="headerlink" title="使用样式表对象"></a>使用样式表对象</h2><p>下面使用样式表对象遍历选择器：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">let myRules = document.styleSheets[0].cssRules,</span><br><span class="line"> p = document.querySelector('p');</span><br><span class="line"></span><br><span class="line">for (i of myRules) {</span><br><span class="line"> if (i.type === 1) {</span><br><span class="line"> p.innerHTML += `<code>${i.selectorText}</code><br>`;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>注意：cssRules是对象。</p>
<p><code>type</code>类型：</p>
<ul>
<li><code>1</code>: STYLE_RULE</li>
<li><code>3</code>: IMPORT_RULE</li>
<li><code>4</code>: MEDIA_RULE</li>
<li><code>5</code>: KEYFRAMES_RULE</li>
</ul>
<blockquote>
<p>完整类型请参考：<a href="https://developer.mozilla.org/en-US/docs/Web/API/CSSRule#Type_constants" target="_blank" rel="noopener">https://developer.mozilla.org/en-US/docs/Web/API/CSSRule#Type_constants</a></p>
</blockquote>
<p>其中<code>selectorText</code>是可写属性，所以我们可以动态修改：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">for (i of myRules) {</span><br><span class="line"> if (i.type === 1) {</span><br><span class="line"> if (i.selectorText === 'a:hover') {</span><br><span class="line"> i.selectorText = 'a:hover, a:active';</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> }</span><br></pre></td></tr></table></figure>
<h2 id="使用CSSOM访问-media规则"><a href="#使用CSSOM访问-media规则" class="headerlink" title="使用CSSOM访问@media规则"></a>使用CSSOM访问@media规则</h2><p>假如有如下属性：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">@media (max-width: 800px) {</span><br><span class="line"> body {</span><br><span class="line"> line-height: 1.2;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> .component {</span><br><span class="line"> float: none;</span><br><span class="line"> margin: 0;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>可以通过<code>conditionText</code>获取：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">let myRules = document.styleSheets[0].cssRules,</span><br><span class="line"> p = document.querySelector('.output');</span><br><span class="line"></span><br><span class="line">for (i of myRules) {</span><br><span class="line"> if (i.type === 4) {</span><br><span class="line"> p.innerHTML += `<code>${i.conditionText}</code><br>`;</span><br><span class="line"> // (max-width: 800px) </span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="使用CSSOM访问-keyframes规则"><a href="#使用CSSOM访问-keyframes规则" class="headerlink" title="使用CSSOM访问@keyframes规则"></a>使用CSSOM访问@keyframes规则</h2><p>假如有如下属性：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">@keyframes exampleAnimation {</span><br><span class="line"> from {</span><br><span class="line"> color: blue;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> 20% {</span><br><span class="line"> color: orange;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> to {</span><br><span class="line"> color: green;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<p>可以通过<code>keyText</code>获取：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line">for (i of myRules) {</span><br><span class="line"> if (i.type === 7) {</span><br><span class="line"> for (j of i.cssRules) {</span><br><span class="line"> p.innerHTML += `<code>${j.keyText}</code><br>`;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">// 0% 20% 100%</span><br></pre></td></tr></table></figure>
<p>您会注意到我的原始CSS使用from并to作为第一个和最后一个关键帧，但keyText属性计算这些0%和100%。keyText也可以设置值。在我的示例样式表中，我可以像这样硬编码：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">// Read the current value (0%)</span><br><span class="line">document.styleSheets[0].cssRules[6].cssRules[0].keyText;</span><br><span class="line"></span><br><span class="line">// Change the value to 10%</span><br><span class="line">document.styleSheets[0].cssRules[6].cssRules[0].keyText = '10%'</span><br><span class="line"></span><br><span class="line">// Read the new value (10%)</span><br><span class="line">document.styleSheets[0].cssRules[6].cssRules[0].keyText;</span><br></pre></td></tr></table></figure>
<p>访问@keyframes规则时可用的另一个属性是name：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">let myRules = document.styleSheets[0].cssRules,</span><br><span class="line"> p = document.querySelector('.output');</span><br><span class="line"></span><br><span class="line">for (i of myRules) {</span><br><span class="line"> if (i.type === 7) {</span><br><span class="line"> p.innerHTML += `<code>${i.name}</code><br>`;</span><br><span class="line"> }</span><br><span class="line">}</span><br><span class="line"></span><br><span class="line">// exampleAnimation</span><br></pre></td></tr></table></figure>
<p>我在这里要提到的最后一件事是能够获取单个关键帧内的特定样式。这是一些带有演示的示例代码：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">let myRules = document.styleSheets[0].cssRules,</span><br><span class="line"> p = document.querySelector('.output');</span><br><span class="line"></span><br><span class="line">for (i of myRules) {</span><br><span class="line"> if (i.type === 7) {</span><br><span class="line"> for (j of i.cssRules) {</span><br><span class="line"> p.innerHTML += `<code>${j.style.color}</code><br>`;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="增加或删除CSSDeclarations规则"><a href="#增加或删除CSSDeclarations规则" class="headerlink" title="增加或删除CSSDeclarations规则"></a>增加或删除CSSDeclarations规则</h2><p>通过<code>insertRule()</code>增加规则：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">let myStylesheet = document.styleSheets[0];</span><br><span class="line">console.log(myStylesheet.cssRules.length); // 8</span><br><span class="line"></span><br><span class="line">document.styleSheets[0].insertRule('article { line-height: 1.5; font-size: 1.5em; }', myStylesheet.cssRules.length);</span><br><span class="line">console.log(document.styleSheets[0].cssRules.length); // 9</span><br></pre></td></tr></table></figure>
<p><code>insertRule()</code>第一个参数是样式字符串，第二个参数是表示您希望插入规则的位置或索引。如果未包括此项，则默认为0（意味着规则将插入规则集合的开头）。如果索引恰好大于rules对象的长度，则会抛出错误。</p>
<p>通过<code>deleteRule()</code>删除规则：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">let myStylesheet = document.styleSheets[0];</span><br><span class="line">console.log(myStylesheet.cssRules.length); // 8</span><br><span class="line"></span><br><span class="line">myStylesheet.deleteRule(3);</span><br><span class="line">console.log(myStylesheet.cssRules.length); // 7</span><br></pre></td></tr></table></figure>
<p>该方法接受一个参数，该参数表示我要删除的规则的索引，参数传入的索引值必须小于cssRules对象的长度，否则将引发错误。</p>
<h2 id="重新访问CSSStyleDeclaration-API"><a href="#重新访问CSSStyleDeclaration-API" class="headerlink" title="重新访问CSSStyleDeclaration API"></a>重新访问CSSStyleDeclaration API</h2><p>记住，<code>CSSRule</code>下的<code>style</code>属性返回<code>CSSStyleDeclaration</code>属性：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line">// Grab the style rules for the body and main elements</span><br><span class="line">let myBodyRule = document.styleSheets[0].cssRules[1].style,</span><br><span class="line"> myMainRule = document.styleSheets[0].cssRules[2].style;</span><br><span class="line"></span><br><span class="line">// Set the bg color on the body</span><br><span class="line">myBodyRule.setProperty('background-color', 'peachpuff');</span><br><span class="line"></span><br><span class="line">// Get the font size of the body</span><br><span class="line">myBodyRule.getPropertyValue('font-size');</span><br><span class="line"></span><br><span class="line">// Get the 5th item in the body's style rule</span><br><span class="line">myBodyRule.item(5);</span><br><span class="line"></span><br><span class="line">// Log the current length of the body style rule (8)</span><br><span class="line">myBodyRule.length;</span><br><span class="line"></span><br><span class="line">// Remove the line height</span><br><span class="line">myBodyRule.removeProperty('line-height');</span><br><span class="line"></span><br><span class="line">// log the length again (7)</span><br><span class="line">myBodyRule.length;</span><br><span class="line"></span><br><span class="line">// Check priority of font-family (empty string)</span><br><span class="line">myBodyRule.getPropertyPriority('font-family');</span><br><span class="line"></span><br><span class="line">// Check priority of margin in the "main" style rule (!important)</span><br><span class="line">myMainRule.getPropertyPriority('margin');</span><br></pre></td></tr></table></figure>
<h2 id="CSSDOM的未来？"><a href="#CSSDOM的未来？" class="headerlink" title="CSSDOM的未来？"></a>CSSDOM的未来？</h2><p>在我在本文中考虑过的所有内容之后，我不得不打破这样的消息，即有一天我们所知道的CSSOM可能已经过时了。</p>
<p>这是因为称为CSS Typed OM的东西，它是Houdini项目的一部分。虽然有些人已经注意到新的Typed OM与目前的CSSOM相比更加冗长，但Eric Bidelman在本文中概述的好处包括：</p>
<ul>
<li>更少的错误</li>
<li>算术运算和单位转换</li>
<li>更好的性能</li>
<li>错误处理</li>
<li>CSS属性名称始终是字符串</li>
</ul>
<p>有关这些功能的完整详细信息和语法的一瞥，请务必查看<a href="https://developers.google.com/web/updates/2018/03/cssom" target="_blank" rel="noopener">完整的文章</a>。</p>
<p>在撰写本文时，<a href="https://drafts.css-houdini.org/css-typed-om/" target="_blank" rel="noopener">CSS Typed OM</a>仅在Chrome中受支持。</p>
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<p>Javascript是单线程单一并发语言，这意味着它可以一次处理一个任务或一次处理一段代码。它有一个单独的调用堆栈，它与堆之类的其他部分一起构成了Javascript并发模型（在V8内部实现）。我们首先来看看这些术语：</p>
<p><img src="../../images/1_ZSFHnq9iMHIApVLcgwczPQ.png" alt="demo"></p>
<p>下面是我总结的一张图片：</p>
<p><img src="../../images/javascript引擎.png" alt="demo"></p>
<p>这里我展开讲，如果需要详细了解请参阅下面参考网址。</p>
<p>下面以一道面试题展开：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line">function Foo() {</span><br><span class="line"> getName = function () { alert (1); };</span><br><span class="line"> return this;</span><br><span class="line">}</span><br><span class="line">Foo.getName = function () { alert (2);};</span><br><span class="line">Foo.prototype.getName = function () { alert (3);};</span><br><span class="line">var getName = function () { alert (4);};</span><br><span class="line">function getName() { alert (5);}</span><br><span class="line"></span><br><span class="line">//请写出以下输出结果：</span><br><span class="line">getName();</span><br><span class="line">Foo().getName();</span><br><span class="line">getName();</span><br></pre></td></tr></table></figure>
<h2 id="执行上下文"><a href="#执行上下文" class="headerlink" title="执行上下文"></a>执行上下文</h2><p>代码开始，引擎创建全局执行上下文：</p>
<ol>
<li><p>创建阶段</p>
<ul>
<li>ThisBinding: 这边的<code>this</code>为window对象</li>
<li>词法环境：<ul>
<li>环境记录：<ul>
<li>Foo: <func></func></li>
<li>getName: <func></func></li>
</ul>
</li>
<li>外部环境引用：<code>null</code></li>
</ul>
</li>
<li>变量环境：<ul>
<li>环境记录：<ul>
<li>getName: undefined</li>
</ul>
</li>
<li>外部环境应用：<globallexicalenvironment></globallexicalenvironment></li>
</ul>
</li>
</ul>
</li>
</ol>
<p>正是由于javascript引擎会在执行上下文之前的创建阶段（即变量提升），所以代码实际上是变成如下：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line">function Foo() {</span><br><span class="line"> getName = function () { alert (1); };</span><br><span class="line"> return this;</span><br><span class="line">}</span><br><span class="line">var getName;//只提升变量声明</span><br><span class="line">function getName() { alert (5);}//提升函数声明，覆盖var的声明</span><br><span class="line"> </span><br><span class="line">Foo.getName = function () { alert (2);};</span><br><span class="line">Foo.prototype.getName = function () { alert (3);};</span><br><span class="line">getName = function () { alert (4);};//最终的赋值再次覆盖function getName声明</span><br></pre></td></tr></table></figure>
<p>所以第一问的答案输出为<code>4</code>。</p>
<ol>
<li>执行阶段</li>
</ol>
<h2 id="调用堆栈"><a href="#调用堆栈" class="headerlink" title="调用堆栈"></a>调用堆栈</h2><p>假设当开始执行到<code>Foo().getName()</code>时，开始进入<code>Foo</code>函数，把<code>Foo</code>函数压入调用堆栈顶部。创建<code>Foo</code>局部执行上下文创建阶段：</p>
<ul>
<li>ThisBinding: 由于这边没有对象调用，故为this为<code>window</code>对象</li>
<li>词法环境：<ul>
<li>环境记录：</li>
<li>外部环境引用：<globallexicalenvironment></globallexicalenvironment></li>
</ul>
</li>
<li>变量环境：<ul>
<li>环境记录：<ul>
<li>getName: function(){ alert(4); }</li>
</ul>
</li>
<li>外部环境应用：<globallexicalenvironment></globallexicalenvironment></li>
</ul>
</li>
</ul>
<p><code>return this</code>返回时，<code>Foo</code>函数弹出栈顶，<code>Foo</code>局部执行上下文销毁。</p>
<p>故执行时第二问答案输出<code>1</code>；第三问因为<code>getName</code>已被第二问中修改，故输出<code>1</code>。</p>
<h2 id="事件循环"><a href="#事件循环" class="headerlink" title="事件循环"></a>事件循环</h2><p>事件循环是指主线程重复从消息队列中取消息、执行的过程。如果遇到同步函数，直接压入调用栈，如果异步代码，则委托给事件队列，然后继续运行代码，当异步处理返回时压入事件队列，主线程在执行完当前循环中的所有代码后，就会到消息队列取出这条消息，并执行它：</p>
<p><img src="../../images/3259161542-575018ce29d44_articlex.png" alt="demo"></p>
<h2 id="参考网址"><a href="#参考网址" class="headerlink" title="参考网址"></a>参考网址</h2><ul>
<li><a href="https://tylermcginnis.com/javascript-visualizer/?code=function%20Foo%28%29%20%7B%0A%20%20%20%20getName%20%3D%20function%20%28%29%20%7B%20alert%20%281%29%3B%20%7D%3B%0A%20%20%20%20return%20this%3B%0A%7D%0AFoo.getName%20%3D%20function%20%28%29%20%7B%20alert%20%282%29%3B%7D%3B%0AFoo.prototype.getName%20%3D%20function%20%28%29%20%7B%20alert%20%283%29%3B%7D%3B%0Avar%20getName%20%3D%20function%20%28%29%20%7B%20alert%20%284%29%3B%7D%3B%0Afunction%20getName%28%29%20%7B%20alert%20%285%29%3B%7D%0A%0A%2F%2F%E8%AF%B7%E5%86%99%E5%87%BA%E4%BB%A5%E4%B8%8B%E8%BE%93%E5%87%BA%E7%BB%93%E6%9E%9C%EF%BC%9A%0AgetName%28%29%3B%0AFoo%28%29.getName%28%29%3B%0AgetName%28%29%3B" target="_blank" rel="noopener">https://tylermcginnis.com/javascript-visualizer/?code=function%20Foo%28%29%20%7B%0A%20%20%20%20getName%20%3D%20function%20%28%29%20%7B%20alert%20%281%29%3B%20%7D%3B%0A%20%20%20%20return%20this%3B%0A%7D%0AFoo.getName%20%3D%20function%20%28%29%20%7B%20alert%20%282%29%3B%7D%3B%0AFoo.prototype.getName%20%3D%20function%20%28%29%20%7B%20alert%20%283%29%3B%7D%3B%0Avar%20getName%20%3D%20function%20%28%29%20%7B%20alert%20%284%29%3B%7D%3B%0Afunction%20getName%28%29%20%7B%20alert%20%285%29%3B%7D%0A%0A%2F%2F%E8%AF%B7%E5%86%99%E5%87%BA%E4%BB%A5%E4%B8%8B%E8%BE%93%E5%87%BA%E7%BB%93%E6%9E%9C%EF%BC%9A%0AgetName%28%29%3B%0AFoo%28%29.getName%28%29%3B%0AgetName%28%29%3B</a></li>
<li><a href="https://mp.weixin.qq.com/s/QljMmVPJ8k7eYB2ynV03LQ" target="_blank" rel="noopener">https://mp.weixin.qq.com/s/QljMmVPJ8k7eYB2ynV03LQ</a></li>
<li><a href="https://medium.com/@gaurav.pandvia/understanding-javascript-function-executions-tasks-event-loop-call-stack-more-part-1-5683dea1f5ec" target="_blank" rel="noopener">https://medium.com/@gaurav.pandvia/understanding-javascript-function-executions-tasks-event-loop-call-stack-more-part-1-5683dea1f5ec</a></li>
<li><a href="https://www.valentinog.com/blog/js-execution-context-call-stack/" target="_blank" rel="noopener">https://www.valentinog.com/blog/js-execution-context-call-stack/</a></li>
<li><a href="https://blog.bitsrc.io/understanding-execution-context-and-execution-stack-in-javascript-1c9ea8642dd0" target="_blank" rel="noopener">https://blog.bitsrc.io/understanding-execution-context-and-execution-stack-in-javascript-1c9ea8642dd0</a></li>
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<h2 id="背景"><a href="#背景" class="headerlink" title="背景"></a>背景</h2><p>公司自己编写的库越来越多，而且之间的关联性比较强，如果某个包升级了版本，其他包也得相对应升级，这样非常的繁琐。</p>
<h2 id="什么是-monorepo-和-multirepo"><a href="#什么是-monorepo-和-multirepo" class="headerlink" title="什么是 monorepo 和 multirepo"></a>什么是 monorepo 和 multirepo</h2><p>在讲lerna之前，我们要先了解一下两个不同的代码管理组织方式 monorepo 和 multirepo：</p>
<ul>
<li><p><code>monorepo</code>：把所有的相关项目放在同一个仓库下，有点类似<code>yarn workspaces</code></p>
</li>
<li><p><code>multirepo</code>：每个子项目拥有自己的 repo</p>
</li>
</ul>
<h2 id="什么是lerna"><a href="#什么是lerna" class="headerlink" title="什么是lerna"></a>什么是lerna</h2><p><a href="https://github.com/lerna/lerna" target="_blank" rel="noopener">lerna</a>是一个管理多个javascript包的工具。它属于<code>monorepo</code>类型，当你的项目有相关联时最好使用<code>monorepo</code>方式进行管理。</p>
<h2 id="以一个简单的示例进行说明"><a href="#以一个简单的示例进行说明" class="headerlink" title="以一个简单的示例进行说明"></a>以一个简单的示例进行说明</h2><p>新建一个<code>testLerna</code>项目：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$ npx lerna init</span><br></pre></td></tr></table></figure>
<p>初始化一个lerna命令，生成以下目录结构：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">testLerna/</span><br><span class="line"> packages/</span><br><span class="line"> lerna.json</span><br><span class="line"> package.json</span><br></pre></td></tr></table></figure>
<p><code>pcakges</code>目录主要放置包，<code>lerna.json</code>为配置文件。</p>
<h2 id="两种模式"><a href="#两种模式" class="headerlink" title="两种模式"></a>两种模式</h2><ul>
<li>Fixed/Locked 模式 (默认)</li>
</ul>
<p>通过在<code>lerna.json</code>中指定<code>version</code>，当你运行<code>lerna publish</code>时，如果其中某一个包至上次发布以来有更新，则将会更新<code>version</code>。</p>
<p>这个模式是babel目前使用的模式，当你想把所有包关联在一起的时候可以考虑使用这种模式，需要注意的是，当其中某个包升级了大版本之后，其他的每个包都会自动升级大版本。</p>
<ul>
<li>Independent mode</li>
</ul>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">lerna init --independent</span><br></pre></td></tr></table></figure>
<p>独立模式允许您更具体地更新每个包的版本，并对一组组件有意义。跟<a href="https://github.com/semantic-release/semantic-release" target="_blank" rel="noopener">semantic-release</a>等工具配合使用会更好。</p>
<blockquote>
<p>已经有结合使用的<a href="https://github.com/atlassian/lerna-semantic-release" target="_blank" rel="noopener">示例</a></p>
</blockquote>
<h2 id="发布"><a href="#发布" class="headerlink" title="发布"></a>发布</h2><p>假设以下项目：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line">packages</span><br><span class="line"> shareui</span><br><span class="line"> shareui-html</span><br><span class="line"> shareui-font</span><br></pre></td></tr></table></figure>
<p>shareui依赖shareui-html，shareui-html依赖shareui-font，可以命令添加：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">$ lerna add shareui-html --scope=shareui</span><br><span class="line">$ lerna add shareui-font --scope=shareui-html</span><br></pre></td></tr></table></figure>
<blockquote>
<p>前提是要关联git，修改registry到公司私库</p>
</blockquote>
<p>git提交到暂存区域，之后通过<code>lerna publish</code>发布：</p>
<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">$ lerna publish</span><br></pre></td></tr></table></figure>
<p>以下情况需要考虑：</p>
<ul>
<li><p>shareui-font升级了，相对应的shareui-html和shareui也要升级？</p>
<p> 运行<code>lerna bootstrap</code>升级对应依赖</p>
</li>
</ul>
<h2 id="参考网址"><a href="#参考网址" class="headerlink" title="参考网址"></a>参考网址</h2><ul>
<li><a href="https://github.com/lerna/lerna" target="_blank" rel="noopener">https://github.com/lerna/lerna</a></li>
<li><a href="https://zhuanlan.zhihu.com/p/33858131" target="_blank" rel="noopener">https://zhuanlan.zhihu.com/p/33858131</a></li>
<li><a href="https://zhuanlan.zhihu.com/p/35237759" target="_blank" rel="noopener">https://zhuanlan.zhihu.com/p/35237759</a></li>
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<h2 id="概述"><a href="#概述" class="headerlink" title="概述"></a>概述</h2><p>ESLint 是在 ECMAScript/JavaScript 代码中识别和报告模式匹配的工具，它的目标是保证代码的一致性和避免错误。在许多方面，它和 JSLint、JSHint 相似，除了少数的例外：</p>
<ul>
<li>ESLint 使用 Espree 解析 JavaScript。</li>
<li>ESLint 使用 AST 去分析代码中的模式</li>
<li>ESLint 是完全插件化的。每一个规则都是一个插件并且你可以在运行时添加更多的规则。</li>