Revision 1028896 of SyntaxError: Malformed formal parameter

<div>{{jsSidebar("Errors")}}</div>

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

<pre class="syntaxbox">
SyntaxError: malformed formal parameter (Firefox)
</pre>

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

<p>{{jsxref("SyntaxError")}}</p>

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

<p>You're using <code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function">Function()</a></code> and passing at least two arguments. The last argument is the source code for the new function you're creating. All the rest make up your new function's argument list.</p>

<p>The argument list is invalid somehow. Perhaps you accidentally picked a keyword like <code>if</code> or <code>var</code> as an argument name, or perhaps there's some stray punctuation in your argument list. Or maybe you accidentally passed an invalid value, like a number or object.</p>

<h2 id="OK_that_fixed_my_problem._But_why_didn't_you_say_that_in_the_first_place">OK, that fixed my problem. But why didn't you say that in the first place?</h2>

<p>Admittedly the wording in the error message is slightly strange. "Formal parameter" is a fancy way of saying "function argument". And we use the word "malformed" because all Firefox engineers are huge fans of 19th-century Gothic horror novels.</p>

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

<h3 id="Invalid_cases">Invalid cases</h3>

<pre class="brush: js example-bad">
var f = Function("x y", "return x + y;");  
// SyntaxError (missing a comma)

var f = Function("x,", "return x;");  
// SyntaxError (extraneous comma)

var f = Function(37, "alert('OK')");
// SyntaxError (numbers can't be argument names)
</pre>

<h3 id="Valid_cases">Valid cases</h3>

<pre class="brush: js example-good">
var f = Function("x, y", "return x + y;");  // correctly punctuated

var f = Function("x", "return x;");

// if you can, avoid using Function - this is much faster
var f = function (x) { return x; };
</pre>

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

<ul>
 <li><code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function">Function()</a></code></li>
 <li><a href="/en-US/docs/Web/JavaScript/Guide/Functions">About functions</a></li>
 <li><a href="https://www.gutenberg.org/ebooks/84"><em>Frankenstein</em> by Mary Wollstonecraft Shelley, full e-text</a> ("Cursed (although I curse myself) be the hands that formed you! You have made me wretched beyond expression. You have left me no power to consider whether I am just to you or not. Begone! Relieve me from the sight of your detested form.")</li>
</ul>