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---
title: Function
slug: Web/JavaScript/Reference/Global_Objects/Function
tags:
- Constructor
- Function
- JavaScript
- NeedsTranslation
- TopicStub
translation_of: Web/JavaScript/Reference/Global_Objects/Function
---
<div>{{JSRef}}</div>
<p>The <strong><code>Function</code> constructor</strong> creates a new <code>Function</code> object. Calling the constructor directly can create functions dynamically, but suffers from security and similar (but far less significant) performance issues to {{jsxref("eval")}}. However, unlike eval, the Function constructor creates functions which execute in the global scope only.</p>
<div>{{EmbedInteractiveExample("pages/js/function-constructor.html")}}</div>
<p>Every JavaScript function is actually a <code>Function</code> object. This can be seen with the code <code>(function(){}).constructor === Function</code> which returns true.</p>
<h2 id="Syntax">Syntax</h2>
<pre class="syntaxbox"><code>new Function ([<var>arg1</var>[, <var>arg2</var>[, ...<var>argN</var>]],] <var>functionBody</var>)</code></pre>
<h3 id="Parameters">Parameters</h3>
<dl>
<dt><code>arg1, arg2, ... arg<em>N</em></code></dt>
<dd>Names to be used by the function as formal argument names. Each must be a string that corresponds to a valid JavaScript identifier or a list of such strings separated with a comma; for example "<code>x</code>", "<code>theValue</code>", or "<code>a,b</code>".</dd>
<dt><code>functionBody</code></dt>
<dd>A string containing the JavaScript statements comprising the function definition.</dd>
</dl>
<h2 id="Description">Description</h2>
<p><code>Function</code> objects created with the <code>Function</code> constructor are parsed when the function is created. This is less efficient than declaring a function with a <a href="/en-US/docs/Web/JavaScript/Reference/Operators/function">function expression</a> or <a href="/en-US/docs/Web/JavaScript/Reference/Statements/function">function statement</a> and calling it within your code because such functions are parsed with the rest of the code.</p>
<p>All arguments passed to the function are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed. Omitting an argument will result in the value of that parameter being <code>undefined</code>.</p>
<p>Invoking the <code>Function</code> constructor as a function (without using the <code>new</code> operator) has the same effect as invoking it as a constructor.</p>
<h2 id="Properties_and_Methods_of_Function">Properties and Methods of <code>Function</code></h2>
<p>The global <code>Function</code> object has no methods or properties of its own. However, since it is a function itself, it does inherit some methods and properties through the prototype chain from {{jsxref("Function.prototype")}}.</p>
<h2 id="Function_prototype_object"><code>Function</code> prototype object</h2>
<h3 id="Properties">Properties</h3>
<div>{{page('/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/prototype', 'Properties')}}</div>
<h3 id="Methods">Methods</h3>
<div>{{page('/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/prototype', 'Methods')}}</div>
<h2 id="Function_instances"><code>Function</code> instances</h2>
<p><code>Function</code> instances inherit methods and properties from {{jsxref("Function.prototype")}}. As with all constructors, you can change the constructor's prototype object to make changes to all <code>Function</code> instances.</p>
<h2 id="Examples">Examples</h2>
<h3 id="Specifying_arguments_with_the_Function_constructor">Specifying arguments with the <code>Function</code> constructor</h3>
<p>The following code creates a <code>Function</code> object that takes two arguments.</p>
<pre class="brush: js">// Example can be run directly in your JavaScript console
// Create a function that takes two arguments and returns the sum of those arguments
var adder = new Function('a', 'b', 'return a + b');
// Call the function
adder(2, 6);
// > 8
</pre>
<p>The arguments "<code>a</code>" and "<code>b</code>" are formal argument names that are used in the function body, "<code>return a + b</code>".</p>
<h3 id="Difference_between_Function_constructor_and_function_declaration">Difference between Function constructor and function declaration</h3>
<p>Functions created with the <code>Function</code> constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the <code>Function</code> constructor was created. This is different from using {{jsxref("eval")}} with code for a function expression.</p>
<pre class="brush: js">var x = 10;
function createFunction1() {
var x = 20;
return new Function('return x;'); // this |x| refers global |x|
}
function createFunction2() {
var x = 20;
function f() {
return x; // this |x| refers local |x| above
}
return f;
}
var f1 = createFunction1();
console.log(f1()); // 10
var f2 = createFunction2();
console.log(f2()); // 20<code>
</code></pre>
<p>While this code works in web browsers, <code>f1()</code> will produce a <code>ReferenceError</code> in Node.js, as <code>x</code> will not be found. This is because the top-level scope in Node is not the global scope, and <code>x</code> will be local to the module.</p>
<h2 id="Specifications">Specifications</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('ES1')}}</td>
<td>{{Spec2('ES1')}}</td>
<td>Initial definition. Implemented in JavaScript 1.0.</td>
</tr>
<tr>
<td>{{SpecName('ES5.1', '#sec-15.3', 'Function')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-function-objects', 'Function')}}</td>
<td>{{Spec2('ES6')}}</td>
<td> </td>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-function-objects', 'Function')}}</td>
<td>{{Spec2('ESDraft')}}</td>
<td> </td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Browser compatibility</h2>
<div>
<p>{{Compat("javascript.builtins.Function")}}</p>
</div>
<h2 id="See_also">See also</h2>
<ul>
<li>{{jsxref("Functions", "Functions and function scope")}}</li>
<li>{{jsxref("Statements/function", "function statement")}}</li>
<li>{{jsxref("Operators/function", "function expression")}}</li>
<li>{{jsxref("Statements/function*", "function* statement")}}</li>
<li>{{jsxref("Operators/function*", "function* expression")}}</li>
<li>{{jsxref("AsyncFunction")}}</li>
<li>{{jsxref("GeneratorFunction")}}</li>
</ul>
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