Revision 1067080 of ReferenceError: 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>There was an unexpected assignment somewhere. This might be due to a mismatch of a <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Assignment_Operators">assignment operator</a> and a <a href="/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators">comparison operator</a>, for example. While a single "<code>=</code>" sign assigns a value to a variable, the "<code>==</code>" or "<code>===</code>" operators compare a value.</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>In the <code>if</code> statement, you want to use a comparison operator ("=="), and for the string concatenation, the plus ("+") operator is needed.</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="/en-US/docs/Web/JavaScript/Reference/Operators/Assignment_Operators">Assignment operators</a></li>
 <li><a href="/en-US/docs/Web/JavaScript/Reference/Operators/Comparison_Operators">Comparison operators</a></li>
</ul>