Revision 980823 of Function

<div>{{JSRef}}</div>

<p>The <strong><code>Function</code> constructor</strong> creates a new <code>Function</code> object. In JavaScript every function is actually a <code>Function</code> object.</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.</p>

<div class="note">
<p><strong>Note:</strong> 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 called. This is different from using {{jsxref("eval")}} with code for a function expression.</p>
</div>

<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/JavaScript/Reference/Global_Objects/Function/prototype', 'Properties')}}</div>

<h3 id="Methods">Methods</h3>

<div>{{page('/en-US/docs/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);
// &gt; 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="A_recursive_shortcut_to_massively_modify_the_DOM">A recursive shortcut to massively modify the DOM</h3>

<p>Creating functions with the <code>Function</code> constructor is one of the ways to dynamically create an indeterminate number of new objects with some executable code into the global scope from a function. The following example (a recursive shortcut to massively modify the DOM) is impossible without the invocation of the <code>Function</code> constructor for each new query if you want to avoid closures.</p>

<pre class="brush: html">
&lt;!doctype html&gt;
&lt;html&gt;
&lt;head&gt;
&lt;meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /&gt;
&lt;title&gt;MDN Example - a recursive shortcut to massively modify the DOM&lt;/title&gt;
&lt;script type="text/javascript"&gt;
var domQuery = (function() {
  var aDOMFunc = [
    Element.prototype.removeAttribute,
    Element.prototype.setAttribute,
    CSSStyleDeclaration.prototype.removeProperty,
    CSSStyleDeclaration.prototype.setProperty
  ];

  function setSomething(bStyle, sProp, sVal) {
    var bSet = Boolean(sVal), fAction = aDOMFunc[bSet | bStyle &lt;&lt; 1],
        aArgs = Array.prototype.slice.call(arguments, 1, bSet ? 3 : 2),
        aNodeList = bStyle ? this.cssNodes : this.nodes;

    if (bSet &amp;&amp; bStyle) { aArgs.push(''); }
    for (
      var nItem = 0, nLen = this.nodes.length;
      nItem &lt; nLen;
      fAction.apply(aNodeList[nItem++], aArgs)
    );
    this.follow = setSomething.caller;
    return this;
  }

  function setStyles(sProp, sVal) { return setSomething.call(this, true, sProp, sVal); }
  function setAttribs(sProp, sVal) { return setSomething.call(this, false, sProp, sVal); }
  function getSelectors() { return this.selectors; };
  function getNodes() { return this.nodes; };

  return (function(sSelectors) {
    var oQuery = new Function('return arguments.callee.follow.apply(arguments.callee, arguments);');
    oQuery.selectors = sSelectors;
    oQuery.nodes = document.querySelectorAll(sSelectors);
    oQuery.cssNodes = Array.prototype.map.call(oQuery.nodes, function(oInlineCSS) { return oInlineCSS.style; });
    oQuery.attributes = setAttribs;
    oQuery.inlineStyle = setStyles;
    oQuery.follow = getNodes;
    oQuery.toString = getSelectors;
    oQuery.valueOf = getNodes;
    return oQuery;
  });
})();
&lt;/script&gt;
&lt;/head&gt;

&lt;body&gt;

&lt;div class="testClass"&gt;Lorem ipsum&lt;/div&gt;
&lt;p&gt;Some text&lt;/p&gt;
&lt;div class="testClass"&gt;dolor sit amet&lt;/div&gt;

&lt;script type="text/javascript"&gt;
domQuery('.testClass')
  .attributes('lang', 'en')('title', 'Risus abundat in ore stultorum')
  .inlineStyle('background-color', 'black')('color', 'white')('width', '100px')('height', '50px');
&lt;/script&gt;
&lt;/body&gt;

&lt;/html&gt;
</pre>

<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>&nbsp;</td>
  </tr>
  <tr>
   <td>{{SpecName('ES6', '#sec-function-objects', 'Function')}}</td>
   <td>{{Spec2('ES6')}}</td>
   <td>&nbsp;</td>
  </tr>
  <tr>
   <td>{{SpecName('ESDraft', '#sec-function-objects', 'Function')}}</td>
   <td>{{Spec2('ESDraft')}}</td>
   <td>&nbsp;</td>
  </tr>
 </tbody>
</table>

<h2 id="Browser_compatibility">Browser compatibility</h2>

<div>{{CompatibilityTable}}</div>

<div id="compat-desktop">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Chrome</th>
   <th>Firefox (Gecko)</th>
   <th>Internet Explorer</th>
   <th>Opera</th>
   <th>Safari</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

<div id="compat-mobile">
<table class="compat-table">
 <tbody>
  <tr>
   <th>Feature</th>
   <th>Android</th>
   <th>Chrome for Android</th>
   <th>Firefox Mobile (Gecko)</th>
   <th>IE Mobile</th>
   <th>Opera Mobile</th>
   <th>Safari Mobile</th>
  </tr>
  <tr>
   <td>Basic support</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
   <td>{{CompatVersionUnknown}}</td>
  </tr>
 </tbody>
</table>
</div>

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

<ul>
 <li>{{jsxref("Functions", "Functions and function scope")}}</li>
 <li>{{jsxref("Function")}}</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("GeneratorFunction")}}</li>
</ul>