This page was translated from English by the community. Learn more and join the MDN Web Docs community.

Element.before()

Experimental: 这是一个实验中的功能
此功能某些浏览器尚在开发中，请参考浏览器兼容性表格以得到在不同浏览器中适合使用的前缀。由于该功能对应的标准文档可能被重新修订，所以在未来版本的浏览器中该功能的语法和行为可能随之改变。

 ChildNode.before 方法可以在ChildNode这个节点的父节点中插入一些列的 Node 或者 DOMString 对象，位置就是在ChildNode节点的前面，DOMString 对象其实和 Text节点一样的方式来完成插入的。

语法

[Throws, Unscopable]
void Element.before((Node or DOMString)... nodes);

Parameters参数

nodes
一系列的 Node 或者 DOMString 

Exceptions

  • HierarchyRequestError: 当节点插入了错误的层级就会出现报错，需要遵循html标签的层级关系，

Examples事例

Inserting an element插入元素节点

var parent = document.createElement("div");
var child = document.createElement("p");
parent.appendChild(child);
var span = document.createElement("span");

child.before(span);

console.log(parent.outerHTML);
// "<div><span></span><p></p></div>"

Inserting text插入文本节点

var parent = document.createElement("div");
var child = document.createElement("p");
parent.appendChild(child);

child.before("Text");

console.log(parent.outerHTML);
// "<div>Text<p></p></div>"

Inserting an element and text同时插入文本和元素

var parent = document.createElement("div");
var child = document.createElement("p");
parent.appendChild(child);
var span = document.createElement("span");

child.before(span, "Text");

console.log(parent.outerHTML);
// "<div><span></span>Text<p></p></div>"

Element.before() is unscopable不可使用区域

The before() 不能配合with声明使用，See Symbol.unscopables for more information.

with(node) {
  before("foo");
}
// ReferenceError: before is not defined

Polyfill

兼容ie9或者更高版本的方法，You can polyfill the before() method in Internet Explorer 9 and higher with the following code:

// from: https://github.com/jserz/js_piece/blob/master/DOM/ChildNode/before()/before().md
(function (arr) {
  arr.forEach(function (item) {
    if (item.hasOwnProperty('before')) {
      return;
    }
    Object.defineProperty(item, 'before', {
      configurable: true,
      enumerable: true,
      writable: true,
      value: function before() {
        var argArr = Array.prototype.slice.call(arguments),
          docFrag = document.createDocumentFragment();

        argArr.forEach(function (argItem) {
          var isNode = argItem instanceof Node;
          docFrag.appendChild(isNode ? argItem : document.createTextNode(String(argItem)));
        });

        this.parentNode.insertBefore(docFrag, this);
      }
    });
  });
})([Element.prototype, CharacterData.prototype, DocumentType.prototype]);

Specification

Specification Status Comment
DOM
Element.before()		 Living Standard Initial definition.

Browser compatibility

We're converting our compatibility data into a machine-readable JSON format. This compatibility table still uses the old format, because we haven't yet converted the data it contains. Find out how you can help! (en-US)

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 54.0 49 (49) ? 39 ?
Feature Android Android Webview Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support 未实现 54.0 49.0 (49) ? 39 ? 54.0

See also