The Function
constructor creates a new Function
object. Calling the constructor directly can create functions dynamically, but suffers from security and similar (but far less significant) performance issues to eval
. However, unlike eval, the Function constructor creates functions which execute in the global scope only.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
Every JavaScript function is actually a Function
object. This can be seen with the code (function(){}).constructor === Function
which returns true.
Syntax
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 with a function expression or function statement and calling it within your code because such functions 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. Omitting an argument will result in the value of that parameter being undefined
.
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.prototype.arguments
- An array corresponding to the arguments passed to a function. This is deprecated as property of
Function
. Use thearguments
object available within the function instead. Function.arity
Used to specifiy the number of arguments expected by the function, but has been removed. Use thelength
property instead.Function.prototype.caller
- Specifies the function that invoked the currently executing function.
Function.prototype.length
- Specifies the number of arguments expected by the function.
Function.prototype.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.prototype.constructor
for more details.
Methods
Function.prototype.apply()
- Calls a function and sets its this to the provided value. Arguments can be passed as an
Array
object. Function.prototype.bind()
- Creates a new function which, when called, has its this set to the provided value, with a given sequence of arguments preceding any provided when the new function was called.
Function.prototype.call()
- Calls a function and sets its this to the provided value. Arguments can be passed as they are.
Function.prototype.isGenerator()
- Returns
true
if the function is a generator; otherwise returnsfalse
. Function.prototype.toSource()
- Returns a string representing the source code of the function. Overrides the
Object.prototype.toSource
method. Function.prototype.toString()
- Returns a string representing the source code of the function. Overrides the
Object.prototype.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
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
".
Difference between Function constructor and function declaration
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 created. This is different from using eval
with code for a function expression.
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
While this code works in web browsers, f1()
will produce a ReferenceError
in Node.js, as x
will not be found. This is because the top-level scope in Node is not the global scope, and x
will be local to the module.
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.0. |
ECMAScript 5.1 (ECMA-262) The definition of 'Function' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Function' in that specification. |
Standard | |
ECMAScript Latest Draft (ECMA-262) The definition of 'Function' in that specification. |
Draft |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Function | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
apply | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
arguments | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
arity | Chrome No support No | Edge No support No | Firefox No support No | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android No support No | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
bind | Chrome Full support 7 | Edge Full support 12 | Firefox Full support 4 | IE Full support 9 | Opera Full support 11.6 | Safari Full support 5.1 | WebView Android Full support 4 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 12 | Safari iOS Full support 6 | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
call | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5.5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
caller | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 8 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
displayName | Chrome No support No | Edge No support No | Firefox Full support 13 | IE No support No | Opera No support No | Safari ? | WebView Android No support No | Chrome Android No support No | Firefox Android Full support 14 | Opera Android No support No | Safari iOS ? | Samsung Internet Android No support No | nodejs No support No |
isGenerator | Chrome No support No | Edge No support No | Firefox No support 5 — 58 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android No support 5 — 58 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
length | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
name | Chrome Full support 15 | Edge Full support 14 | Firefox Full support 1 | IE No support No | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
prototype | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 4 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
toSource | Chrome No support No | Edge No support No | Firefox Full support 1 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android Full support 4 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No | nodejs No support No |
toString | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 5 | Opera Full support Yes | Safari Full support Yes | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- Non-standard. Expect poor cross-browser support.
- Non-standard. Expect poor cross-browser support.
- Deprecated. Not for use in new websites.
- Deprecated. Not for use in new websites.