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---
title: Strict equality (===)
slug: Web/JavaScript/Reference/Operators/Strict_equality
translation_of: Web/JavaScript/Reference/Operators/Strict_equality
---
<div>{{jsSidebar("Operators")}}</div>
<p>全等运算符 (===) 会检查它的两个操作数是否相等，并且返回一个布尔值结果。与相等运算符不同，全等运算符总是认为不同类型的操作数是不同的。</p>
<div>{{EmbedInteractiveExample("pages/js/expressions-strict-equality.html")}}</div>
<div class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone <a href="https://github.com/mdn/interactive-examples">https://github.com/mdn/interactive-examples</a> and send us a pull request.</div>
<h2 id="语法">语法</h2>
<pre class="syntaxbox">x === y</pre>
<h2 id="描述">描述</h2>
<p>全等运算符（<code>===</code>和 <code>!==</code>）使用<a class="external external-icon" href="http://www.ecma-international.org/ecma-262/5.1/#sec-11.9.6" rel="noopener">全等比较算法</a>来比较两个操作数。</p>
<ul>
<li>如果操作数的类型不同，则返回 <code>false</code>。</li>
<li>如果两个操作数都是对象，只有当它们指向同一个对象时才返回 <code>true</code>。</li>
<li>如果两个操作数都为 <code>null</code>，或者两个操作数都为 <code>undefined</code>，返回 <code>true</code>。</li>
<li>如果两个操作数有任意一个为 <code>NaN</code>，返回 <code>false</code>。</li>
<li>否则，比较两个操作数的值：
<ul>
<li>数字类型必须拥有相同的数值。<code>+0</code> 和 <code>-0</code> 会被认为是相同的值。</li>
<li>字符串类型必须拥有相同顺序的相同字符。</li>
<li>布尔运算符必须同时为 <code>true</code> 或同时为 <code>false</code>。</li>
</ul>
</li>
</ul>
<p>全等运算符与<a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Equality">相等运算符</a>（<code>==</code>）最显著的区别是，如果操作数的类型不同，<code>== </code>运算符会在比较之前尝试将它们转换为相同的类型。</p>
<h2 id="例子">例子</h2>
<h3 id="比较相同类型的操作数">比较相同类型的操作数</h3>
<pre class="brush: js">console.log("hello" === "hello"); // true
console.log("hello" === "hola"); // false
console.log(3 === 3); // true
console.log(3 === 4); // false
console.log(true === true); // true
console.log(true === false); // false
console.log(null === null); // true</pre>
<h3 id="比较不同类型的操作数">比较不同类型的操作数</h3>
<pre class="brush: js">console.log("3" === 3); // false
console.log(true === 1); // false
console.log(null === undefined); // false</pre>
<h3 id="比较对象">比较对象</h3>
<pre class="brush: js">const object1 = {
name: "hello"
}
const object2 = {
name: "hello"
}
console.log(object1 === object2); // false
console.log(object1 === object1); // true</pre>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
<thead>
<tr>
<th scope="col">Specification</th>
</tr>
</thead>
<tbody>
<tr>
<td>{{SpecName('ESDraft', '#sec-equality-operators', 'Equality operators')}}</td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p>{{Compat("javascript.operators.strict_equality")}}</p>
<h2 id="See_also">See also</h2>
<ul>
<li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Equality">Equality operator</a></li>
<li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Inequality">Inequality operator</a></li>
<li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Strict_inequality">Strict inequality operator</a></li>
</ul>
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