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---
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
---
<div>{{APIRef("DOM")}} {{SeeCompatTable}}</div>
<p> <code><strong>ChildNode</strong></code><strong><code>.before</code></strong> 方法可以在<code>ChildNode这个节点的父节点中插入一些列的</code> {{domxref("Node")}} 或者 {{domxref("DOMString")}} 对象，位置就是在<code>ChildNode节点的前面，</code>{{domxref("DOMString")}} 对象其实和 {{domxref("Text")}}节点一样的方式来完成插入的。</p>
<h2 id="语法">语法</h2>
<pre class="syntaxbox">[Throws, Unscopable]
void Element.before((Node or DOMString)... nodes);
</pre>
<h3 id="Parameters参数">Parameters参数</h3>
<dl>
<dt><code>nodes</code></dt>
<dd>一系列的 {{domxref("Node")}} 或者 {{domxref("DOMString")}} </dd>
</dl>
<h3 id="Exceptions">Exceptions</h3>
<ul>
<li>{{domxref("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，</li>
</ul>
<h2 id="Examples事例">Examples事例</h2>
<h3 id="Inserting_an_element插入元素节点">Inserting an element插入元素节点</h3>
<pre class="brush: js">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>"
</pre>
<h3 id="Inserting_text插入文本节点">Inserting text插入文本节点</h3>
<pre class="brush: js">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>"</pre>
<h3 id="Inserting_an_element_and_text同时插入文本和元素">Inserting an element and text同时插入文本和元素</h3>
<pre class="brush: js">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>"</pre>
<h3 id="Element.before()_is_unscopable不可使用区域"><code>Element.before()</code> is unscopable不可使用区域</h3>
<p>The <code>before()</code> 不能配合with声明使用，See {{jsxref("Symbol.unscopables")}} for more information.</p>
<pre class="brush: js">with(node) {
before("foo");
}
// ReferenceError: before is not defined </pre>
<h2 id="Polyfill">Polyfill</h2>
<p>兼容ie9或者更高版本的方法，You can polyfill the <code>before() method</code> in Internet Explorer 9 and higher with the following code:</p>
<pre class="brush: js">// 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]);</pre>
<h2 id="Specification">Specification</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{SpecName('DOM WHATWG', '#dom-childnode-before', 'Element.before()')}}</td>
<td>{{Spec2('DOM WHATWG')}}</td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<p>{{CompatibilityTable}}</p>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatChrome(54.0)}}</td>
<td>{{CompatGeckoDesktop(49)}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatOpera(39)}}</td>
<td>{{CompatUnknown}}</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Android Webview</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
<th>Chrome for Android</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatNo}}</td>
<td>{{CompatChrome(54.0)}}</td>
<td>{{CompatGeckoMobile(49)}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatOpera(39)}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatChrome(54.0)}}</td>
</tr>
</tbody>
</table>
</div>
<h2 id="See_also">See also</h2>
<ul>
<li>{{domxref("ChildNode")}} and {{domxref("ParentNode")}}</li>
<li>{{domxref("ChildNode.after()")}}</li>
<li>{{domxref("ParentNode.append()")}}</li>
<li>{{domxref("Node.appendChild()")}}</li>
<li>{{domxref("Node.insertBefore()")}}</li>
<li>{{domxref("NodeList")}}</li>
</ul>
|
