---
title: 'ReferenceError: invalid assignment left-hand side'
slug: Web/JavaScript/Reference/Errors/Invalid_assignment_left-hand_side
tags:
  - Errors
  - JavaScript
  - ReferenceError
translation_of: Web/JavaScript/Reference/Errors/Invalid_assignment_left-hand_side
---
<div>{{jsSidebar("Errors")}}</div>

<h2 id="Message">Message</h2>

<pre class="syntaxbox">ReferenceError: invalid assignment left-hand side
</pre>

<h2 id="Error_type">Error type</h2>

<p>{{jsxref("ReferenceError")}}.</p>

<h2 id="What_went_wrong">What went wrong?</h2>

<p>有时会出现不可预料的赋值情况。这可能是因为<a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Assignment_Operators">赋值运算符</a>或<a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators">比较运算符</a>不匹配的缘故。正确的是，使用“=”号将值赋给一个变量，使用“==”或者“===”来比较一个值。</p>

<h2 id="Examples">Examples</h2>

<pre class="brush: js example-bad">if (Math.PI = 3 || Math.PI = 4) {
  console.log('no way!');
}
// ReferenceError: invalid assignment left-hand side

var str = 'Hello, '
+= 'is it me '
+= 'you\'re looking for?';
// ReferenceError: invalid assignment left-hand side
</pre>

<p>在 <code>if</code> 语句中，你要使用比较运算符("==")，而在字符串连接中，使用加号运算符("+")。</p>

<pre class="brush: js example-good">if (Math.PI == 3 || Math.PI == 4) {
  console.log('no way!');
}

var str = 'Hello, '
+ 'from the '
+ 'other side!';
</pre>

<h2 id="See_also">See also</h2>

<ul>
 <li><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Assignment_Operators">赋值运算符</a></li>
 <li><a href="/zh-CN/docs/Web/JavaScript/Reference/Operators/Comparison_Operators">比较运算符</a></li>
</ul>