--- title: Element.before() slug: Web/API/Element/before tags: - API - DOM - Method - Node - Reference translation_of: Web/API/Element/before original_slug: Web/API/ChildNode/before browser-compat: api.Element.before ---
{{APIRef("DOM")}} {{SeeCompatTable}}

 ChildNode.before 方法可以在ChildNode这个节点的父节点中插入一些列的 {{domxref("Node")}} 或者 {{domxref("DOMString")}} 对象，位置就是在ChildNode节点的前面，{{domxref("DOMString")}} 对象其实和 {{domxref("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 {{domxref("Node")}} 或者 {{domxref("DOMString")}} 

Exceptions

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 {{jsxref("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
{{SpecName('DOM WHATWG', '#dom-childnode-before', 'Element.before()')}} {{Spec2('DOM WHATWG')}} Initial definition.

Browser compatibility

{{Compat("api.Element.before")}}

See also