Function

Summary

The Function constructor creates a new Function object. In JavaScript every function is actually a Function object.

Constructor

new Function ([arg1[, arg2[, ...argN]],] functionBody)

Parameters

arg1, arg2, ... argN
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 "x", "theValue", or "a,b".
functionBody
A string containing the JavaScript statements comprising the function definition.

Description

Function objects created with the Function constructor are parsed when the function is created. This is less efficient than declaring a function and calling it within your code, because functions declared with the function statement are parsed with the rest of the code.

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.

Note: Functions created with the Function 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 Function constructor was called. This is different from using eval  with code for a function expression. 

Invoking the Function constructor as a function (without using the new operator) has the same effect as invoking it as a constructor.

Properties and Methods of Function

The global Function 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 Function.prototype.

Function prototype object

Properties

Function.arguments
An array corresponding to the arguments passed to a function. This is deprecated as property of Function, use the arguments object available within the function instead.
Function.arity
Used to specifiy the number of arguments expected by the function, but has been removed. Use the length property instead.
Function.caller
Specifies the function that invoked the currently executing function.
Function.length
Specifies the number of arguments expected by the function.
Function.name
The name of the function.
Function.displayName
The display name of the function.
Function.prototype.constructor
Specifies the function that creates an object's prototype. See Object.constructor for more details.
Properties inherited from Object:

Methods

Function.prototype.apply()
Applies the method of another object in the context of a different object (the calling object); arguments can be passed as an Array object.
Function.prototype.bind()
Creates a new function which, when called, itself calls this function in the context of the provided value, with a given sequence of arguments preceding any provided when the new function was called.
Function.prototype.call()
Calls (executes) a method of another object in the context of a different object (the calling object); arguments can be passed as they are.
Function.prototype.isGenerator()
Returns true if the function is a generator; otherwise returns false.
Function.prototype.toSource()
Returns a string representing the source code of the function. Overrides the Object.toSource method.
Function.prototype.toString()
Returns a string representing the source code of the function. Overrides the Object.toString method.

Function instances

Function instances inherit methods and properties from Function.prototype. As with all constructors, you can change the constructor's prototype object to make changes to all Function instances.

Examples

Example: Specifying arguments with the Function constructor

The following code creates a Function object that takes two arguments.

// 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

The arguments "a" and "b" are formal argument names that are used in the function body, "return a + b".

Example: A recursive shortcut to massively modify the DOM

Creating functions with the Function 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 Function constructor for each new query if you want to avoid closures.

<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>MDN Example - a recursive shortcut to massively modify the DOM</title>
<script type="text/javascript">
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 << 1],
         aArgs = Array.prototype.slice.call(arguments, 1, bSet ? 3 : 2),
         aNodeList = bStyle ? this.cssNodes : this.nodes;

    if (bSet && bStyle) { aArgs.push(""); }
    for (
      var nItem = 0, nLen = this.nodes.length;
      nItem < 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;
  });
})();
</script>
</head>

<body>

<div class="testClass">Lorem ipsum</div>
<p>Some text</p>
<div class="testClass">dolor sit amet</div>

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

</html>

Specifications

Specification Status Comment
ECMAScript 1st Edition. Implemented in JavaScript 1.0 Standard Initial definition.
ECMAScript Language Specification 5.1th Edition (ECMA-262) Standard  
ECMAScript Language Specification 6th Edition (ECMA-262) Draft  

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

See also