Function

Every JavaScript function is actually a Function object. This can be seen with the code (function(){}).constructor === Function, which returns true.

Constructor

Function()

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

Function.prototype.arguments Deprecated

An array corresponding to the arguments passed to a function. This is deprecated as a property of Function. Use the arguments object (available within the function) instead.

Function.prototype.caller Deprecated

Specifies the function that invoked the currently executing function. This property is deprecated, and is only functional for some non-strict functions.

Function.prototype.displayName

The display name of the function.

Function.prototype.length

Specifies the number of arguments expected by the function.

Function.prototype.name

The name of the function.

Instance methods

Function.prototype.apply()

Calls a function with a given this value and optional arguments provided as an array (or an array-like object).

Function.prototype.bind()

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.

Function.prototype.call()

Calls a function with a given this value and optional arguments.

Function.prototype.toString()

Returns a string representing the source code of the function. Overrides the Object.prototype.toString method.

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.

const x = 10;

function createFunction1() {
    const x = 20;
    return new Function('return x;'); // this |x| refers global |x|
}

function createFunction2() {
    const x = 20;
    function f() {
        return x; // this |x| refers 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 Language Specification
# sec-function-objects

Browser compatibility

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See also