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Function

The Function creates a new Function object. Calling the constructor directly can create functions dynamically, but suffers from security and performance issues similar to eval.

Every JavaScript function is actually a Function object.

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.

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.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 (executes) 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 returns false.
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 called. 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

Specifications

Browser compatibility

Feature Chrome Edge Firefox Internet Explorer Opera Safari
Basic support Yes Yes Yes Yes Yes Yes
arguments Yes Yes Yes Yes Yes Yes
arity No No No No No No
caller Yes Yes 1 8 Yes Yes
displayName ? ? 13 ? ? ?
length Yes Yes Yes Yes Yes Yes
name 15 Yes Yes No Yes Yes
prototype Yes Yes Yes Yes Yes Yes
apply Yes Yes Yes Yes Yes Yes
bind 7 Yes 4 9 11.6 5.1
call Yes Yes Yes Yes Yes Yes
isGenerator No No 5 — 58 No No No
toSource No No Yes No No No
toString Yes Yes Yes Yes Yes Yes
Feature Android webview Chrome for Android Edge mobile Firefox for Android Opera Android iOS Safari Samsung Internet
Basic support Yes Yes Yes Yes Yes Yes ?
arguments Yes Yes Yes Yes Yes Yes ?
arity No No No No No No ?
caller Yes Yes Yes 4 Yes Yes ?
displayName ? ? ? 14 ? ? ?
length Yes Yes Yes Yes Yes Yes ?
name Yes Yes Yes Yes Yes Yes ?
prototype Yes Yes Yes Yes Yes Yes ?
apply Yes Yes Yes Yes Yes Yes ?
bind 4 1 Yes 4 11.5 6 ?
call Yes Yes Yes Yes Yes Yes ?
isGenerator No No No 5 — 58 No No ?
toSource No No No Yes No No ?
toString Yes Yes Yes Yes Yes Yes ?

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function