Function - JavaScript | MDN (original) (raw)
Baseline
Widely available *
The Function
object provides methods for functions. In JavaScript, every function is actually a Function
object.
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 that execute in the global scope only.
Instance properties
These properties are defined on Function.prototype
and shared by all Function
instances.
Function.prototype.arguments Deprecated Non-standard
Represents the arguments passed to this function. For strict, arrow, async, and generator functions, accessing the arguments
property throws a TypeError. Use the arguments object inside function closures instead.
Function.prototype.caller Deprecated Non-standard
Represents the function that invoked this function. For strict, arrow, async, and generator functions, accessing the caller
property throws a TypeError.
Function.prototype.constructor
The constructor function that created the instance object. For Function
instances, the initial value is the Function constructor.
These properties are own properties of each Function
instance.
displayName Non-standard Optional
The display name of the function.
Specifies the number of arguments expected by the function.
The name of the function.
Used when the function is used as a constructor with the new operator. It will become the new object's prototype.
Instance methods
Calls a function with a given this
value and optional arguments provided as an array (or an array-like object).
Creates a new function that, when called, has its this
keyword set to a provided value, optionally with a given sequence of arguments preceding any provided when the new function is called.
Calls a function with a given this
value and optional arguments.
Returns a string representing the source code of the function. Overrides the Object.prototype.toString method.
Function.prototypeSymbol.hasInstance
Specifies the default procedure for determining if a constructor function recognizes an object as one of the constructor's instances. Called by the instanceof operator.
Examples
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.
// Create a global property with `var`
var x = 10;
function createFunction1() {
const x = 20;
return new Function("return x;"); // this `x` refers to global `x`
}
function createFunction2() {
const x = 20;
function f() {
return x; // this `x` refers to the local `x` above
}
return f;
}
const f1 = createFunction1();
console.log(f1()); // 10
const 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 |
---|
ECMAScript® 2026 Language Specification # sec-function-objects |