IE 9。现在可以加载文本文件并设置样式。innerHTML属性。所以本质上你现在可以通过ajax加载一个css文件(并获得回调)，然后像这样设置样式标签内的文本。

这适用于其他浏览器，不确定多久以前。但只要你不需要支持IE8，它就可以工作。

// RESULT: doesn't work in IE8 and below. Works in IE9 and other browsers.
$(document).ready(function() {
    // we want to load the css as a text file and append it with a style.
    $.ajax({
        url:'myCss.css',
        success: function(result) {
            var s = document.createElement('style');
            s.setAttribute('type', 'text/css');
            s.innerHTML = result;
            document.getElementsByTagName("head")[0].appendChild(s);
        },
        fail: function() {
            alert('fail');
        }
    })
});

然后你可以让它取出一个外部文件，比如mycss。css

.myClass { background:#F00; }

这里有一个选项:

var style = document.createElement（'style'）; style.type = 'text/css'; style.innerHTML = '.cssClass { color： #f00; }'; document.getElementsByTagName（'head'）[0].appendChild（style）; document.getElementById（'someElementId'）.className = 'cssClass'; <div id=“someElementId”>test text</div>

通过查看答案，最明显和最直接的是缺少:使用document.write()写出你需要的CSS块。

下面是一个例子(在codepen上查看:http://codepen.io/ssh33/pen/zGjWga):

<style>
   @import url(http://fonts.googleapis.com/css?family=Open+Sans:800);
   .d, body{ font: 3vw 'Open Sans'; padding-top: 1em; }
   .d {
       text-align: center; background: #aaf;
       margin: auto; color: #fff; overflow: hidden; 
       width: 12em; height: 5em;
   }
</style>

<script>
   function w(s){document.write(s)}
   w("<style>.long-shadow { text-shadow: ");
   for(var i=0; i<449; i++) {
      if(i!= 0) w(","); w(i+"px "+i+"px #444");
   }
   w(";}</style>");
</script> 

<div class="d">
    <div class="long-shadow">Long Shadow<br> Short Code</div>
</div>

https://jsfiddle.net/xk6Ut/256/

在JavaScript中动态创建和更新CSS类的一个选项:

使用样式元素创建CSS节 使用样式元素的ID，以便我们可以更新CSS 类

…

function writeStyles(styleName, cssText) {
    var styleElement = document.getElementById(styleName);
    if (styleElement) 
             document.getElementsByTagName('head')[0].removeChild(
        styleElement);
    styleElement = document.createElement('style');
    styleElement.type = 'text/css';
    styleElement.id = styleName;
    styleElement.innerHTML = cssText;
    document.getElementsByTagName('head')[0].appendChild(styleElement);
}

...

    var cssText = '.testDIV{ height:' + height + 'px !important; }';
    writeStyles('styles_js', cssText)

一个可以帮助您完成任务的有趣项目是JSS。

JSS是一个CSS的创作工具，它允许你使用JavaScript以一种声明性的、无冲突的和可重用的方式描述样式。它可以在浏览器、服务器端或在构建时在Node中编译。

JSS库允许您使用.attach()函数在DOM/head部分中进行注入。

Repl在线版本评估。

更多关于JSS的信息。

一个例子:

// Use plugins.
jss.use(camelCase())

// Create your style.
const style = {
  myButton: {
    color: 'green'
  }
}

// Compile styles, apply plugins.
const sheet = jss.createStyleSheet(style)

// If you want to render on the client, insert it into DOM.
sheet.attach()

YUI拥有迄今为止我所见过的最好的样式表实用程序。我鼓励你去看看，但这里有一个味道:

// style element or locally sourced link element
var sheet = YAHOO.util.StyleSheet(YAHOO.util.Selector.query('style',null,true));

sheet = YAHOO.util.StyleSheet(YAHOO.util.Dom.get('local'));


// OR the id of a style element or locally sourced link element
sheet = YAHOO.util.StyleSheet('local');


// OR string of css text
var css = ".moduleX .alert { background: #fcc; font-weight: bold; } " +
          ".moduleX .warn  { background: #eec; } " +
          ".hide_messages .moduleX .alert, " +
          ".hide_messages .moduleX .warn { display: none; }";

sheet = new YAHOO.util.StyleSheet(css);

There are obviously other much simpler ways of changing styles on the fly such as those suggested here. If they make sense for your problem, they might be best, but there are definitely reasons why modifying CSS is a better solution. The most obvious case is when you need to modify a large number of elements. The other major case is if you need your style changes to involve the cascade. Using the DOM to modify an element will always have a higher priority. It's the sledgehammer approach and is equivalent to using the style attribute directly on the HTML element. That is not always the desired effect.