js修改元素样式

- JS修改样式的九种方式
- - 1.直接设置style的属性
  - 2.直接设置属性
  - 3.设置style的属性
  - 4.使用setProperty
  - 5.改变class （推荐）
  - 6.设置cssText
  - 7.引入css样式文件
  - 8.使用addRule、insertRule
  - 9、通过classList控制样式

JS修改样式的九种方式

1.直接设置style的属性

style属性可以设置或返回元素的内联样式,对于更改同一个元素的同一种样式，设置style属性的优先级较高

语法：element.style.property = value
property为CSS属性名，如：color，margin。如果属性名原来包含“-”，则需转换为小驼峰形式，如：backgroundColor，marginLeft。

var box = document.querySelector('div')
box.style.color = "#fff" // 将元素中文字设置为白色 
box.style.marginLeft = "100px" // 将元素左外边距设置为100px

某些情况用这个设置 !important值无效

如果属性有’-'号，就写成驼峰的形式（如textAlign）如果想保留 - 号，就中括号的形式

element.style.height = '100px';

2.直接设置属性

只能用于某些属性，相关样式会自动识别

element.setAttribute('height', 100);
element.setAttribute('height', '100px');

3.设置style的属性

element.setAttribute('style', 'height: 100px !important');

4.使用setProperty

如果要设置!important，推荐用这种方法设置第三个参数

element.style.setProperty('height', '300px', 'important');

5.改变class （推荐）

通过改变伪元素父级的class来动态更改伪元素的样式

element.className = 'blue';
element.className += 'blue fb';

6.设置cssText

element.style.cssText = 'height: 100px !important';
element.style.cssText += 'height: 100px !important';

7.引入css样式文件

创建引入新的css样式文件

 function addNewStyle(newStyle) {
            var styleElement = document.getElementById('styles_js');
        <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>styleElement<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
            styleElement <span class="token operator">&#61;</span> document<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span><span class="token string">&#39;style&#39;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            styleElement<span class="token punctuation">.</span>type <span class="token operator">&#61;</span> <span class="token string">&#39;text/css&#39;</span><span class="token punctuation">;</span>
            styleElement<span class="token punctuation">.</span>id <span class="token operator">&#61;</span> <span class="token string">&#39;styles_js&#39;</span><span class="token punctuation">;</span>
            document<span class="token punctuation">.</span><span class="token function">getElementsByTagName</span><span class="token punctuation">(</span><span class="token string">&#39;head&#39;</span><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><span class="token function">appendChild</span><span class="token punctuation">(</span>styleElement<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
        
        styleElement<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>document<span class="token punctuation">.</span><span class="token function">createTextNode</span><span class="token punctuation">(</span>newStyle<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>

    <span class="token function">addNewStyle</span><span class="token punctuation">(</span><span class="token string">&#39;.box {height: 100px !important;}&#39;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

8.使用addRule、insertRule

// 在原有样式操作
        document.styleSheets[0].addRule('.box', 'height: 100px');
        document.styleSheets[0].insertRule('.box {height: 100px}', 0);
    <span class="token comment">// 或者插入新样式时操作</span>
    <span class="token keyword">var</span> styleEl <span class="token operator">&#61;</span> document<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span><span class="token string">&#39;style&#39;</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
        styleSheet <span class="token operator">&#61;</span> styleEl<span class="token punctuation">.</span>sheet<span class="token punctuation">;</span>

    styleSheet<span class="token punctuation">.</span><span class="token function">addRule</span><span class="token punctuation">(</span><span class="token string">&#39;.box&#39;</span><span class="token punctuation">,</span> <span class="token string">&#39;height: 100px&#39;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    styleSheet<span class="token punctuation">.</span><span class="token function">insertRule</span><span class="token punctuation">(</span><span class="token string">&#39;.box {height: 100px}&#39;</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    document<span class="token punctuation">.</span>head<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>styleEl<span class="token punctuation">)</span><span class="token punctuation">;</span>

9、通过classList控制样式

classList属性返回一个元素类属性集合（这里可以简单理解为类名的集合），通过使用classList中的方法可以方便的访问和控制元素类名，达到控制样式的目的

classList常用方法介绍：

名称	描述
`add(class1, class2, …)`	添加一个或多个类名
`remove(class1, class2, …)`	移除一个或多个类名
`replace(oldClass, newClass)`	替换类名
`contains(class)`	判定类名是否存在，返回布尔值
`toggle(class, true\|false)`	如果类名存在，则移除它，否则添加它，第二个参数代表无论类名是否存在，强制添加（`true`）或删除（`false`）

<div class="box">classList test</div>
<script>
  var box = document.querySelector('.box')
  box.classList.add('box1', 'box2')    // [box] => [box, box1, box2]
  box.classList.remove('box1', 'box2') // [box, box1, box2] => [box]
  box.classList.replace('box', 'box2')  // [box] => [box2]
  box.classList.contains('box1')  // 当前元素不包含类名box1，返回false
  box.classList.toggle('active')   // [box2] => [box2, active]
</script>

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