How to dynamically insert CSS in JavaScript_javascript skills

When writing components, sometimes I want to encapsulate some CSS styles related to component features in JS, so that they are more cohesive and easy to change. JS dynamically inserts CSS in two steps: Create 1. A style object
2. Use the insertRule or addRule method of stylesheet to add styles

1. View the style sheet

Look at document.styleSheets first and open a page at will

The first three are CSS files introduced through link tags, and the fourth is CSS inlined in the page through style tags. It has the following attributes

Each cssRule has the following attributes

The cssText is exactly the source code written in style.

2. Dynamically insert CSS
First, you need to create a style object and return its stylesheet object

/*
 * 创建一个 style， 返回其 stylesheet 对象
 * 注意：IE6/7/8中使用 style.stylesheet，其它浏览器 style.sheet
 */
function createStyleSheet() {
 var head = document.head || document.getElementsByTagName('head')[0];
 var style = document.createElement('style');
 style.type = 'text/css';
 head.appendChild(style);
 return style.sheet ||style.styleSheet;
}

Add the function addCssRule as follows

/*
 * 动态添加 CSS 样式
 * @param selector {string} 选择器
 * @param rules {string} CSS样式规则
 * @param index {number} 插入规则的位置, 靠后的规则会覆盖靠前的
 */
function addCssRule(selector, rules, index) {
 index = index || 0;
 if (sheet.insertRule) { 
  sheet.insertRule(selector + "{" + rules + "}", index); 
 } else if (sheet.addRule) { 
  sheet.addRule(selector, rules, index); 
 }
}

It should be noted that standard browsers support insertRule, and lower versions of IE support addRule.
The complete code is as follows

/*
 * 动态添加 CSS 样式
 * @param selector {string} 选择器
 * @param rules {string} CSS样式规则
 * @param index {number} 插入规则的位置, 靠后的规则会覆盖靠前的
 */
var addCssRule = function() {
 // 创建一个 style， 返回其 stylesheet 对象
 // 注意：IE6/7/8中使用 style.stylesheet，其它浏览器 style.sheet
 function createStyleSheet() {
  var head = document.head || document.getElementsByTagName('head')[0];
  var style = document.createElement('style');
  style.type = 'text/css';
  head.appendChild(style);
  return style.sheet ||style.styleSheet;
 }
 
 // 创建 stylesheet 对象
 var sheet = createStyleSheet();
 
 // 返回接口函数
 return function(selector, rules, index) {
  index = index || 0;
  if (sheet.insertRule) { 
   sheet.insertRule(selector + "{" + rules + "}", index); 
  } else if (sheet.addRule) { 
   sheet.addRule(selector, rules, index); 
  }
 }
}();

If it only supports mobile terminals or modern browsers, you can remove the code judged by lower versions of IE

/*
 * 动态添加 CSS 样式
 * @param selector {string} 选择器
 * @param rules {string} CSS样式规则
 * @param index {number} 插入规则的位置, 靠后的规则会覆盖靠前的，默认在后面插入
 */
var addCssRule = function() {
 // 创建一个 style， 返回其 stylesheet 对象
 function createStyleSheet() {
  var style = document.createElement('style');
  style.type = 'text/css';
  document.head.appendChild(style);
  return style.sheet;
 }
 
 // 创建 stylesheet 对象
 var sheet = createStyleSheet();
 
 // 返回接口函数
 return function(selector, rules, index) {
  index = index || 0;
  sheet.insertRule(selector + "{" + rules + "}", index);
 }
}();

The above is the method of dynamically inserting CSS in JavaScript. I hope it will be helpful to everyone's learning.