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Function

Function constructor.

Installation

npm install @stdlib/function-ctor

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var Function = require( '@stdlib/function-ctor' );

Function( [...argNames,] body )

Returns a new function object.

var greet = new Function( 'name', 'return "Hello, "+name+"!"' );

var v = greet( 'Jane' );
// returns 'Hello, Jane!'

Argument names must be strings corresponding to valid JavaScript parameters (i.e., a plain identifier, or, in environments supporting such parameters, a rest parameter or destructured parameter, optionally with a default).

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Properties

Function.prototype.length

A number representing the number of arguments expected by the function.

var greet = new Function( 'name', 'return "Hello, "+name+"!"' );
var v = greet.length;
// returns 1

Function.prototype.name

Read-only property representing the name of the function.

function greet( name ) {
    return 'Hello, '+name+'!';
}
var v = greet.name;
// returns 'greet'

// Functions created with the Function constructor are anonymous:
var fcn = new Function( 'name', 'return "Hello, "+name+"!"' );
v = fcn.name;
// returns 'anonymous'

Function.prototype.prototype

Read-only property representing the prototype of the function.

function greet( name ) {
    return 'Hello, '+name+'!';
}
var proto = greet.prototype;
// returns {}

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Methods

Function.prototype.apply( thisArg, args )

Calls the specified function with the given this argument and arguments provided as an array-like object.

function add( x, y ) {
    return this.initial + x + y;
}

var ctx = {
    'initial': 10
};

var v = add.apply( ctx, [ 1, 2 ] );
// returns 13

Function.prototype.bind( thisArg[, arg1[, arg2[, ...]]] )

Returns a new function which invokes the original function with the given this value and arguments.

function add( x, y ) {
    return x + y;
}
var add1 = add.bind( null, 1 );

var v = add1( 2 );
// returns 3

Function.prototype.call( thisArg[, arg1[, arg2[, ...]]] )

Calls the specified function with the given this value and arguments.

function add( x, y ) {
    return this.initial + x + y;
}

var ctx = {
    'initial': 10
};

var v = add.call( ctx, 1, 2 );
// returns 13

Function.prototype.toString()

Returns a string representing the function.

function add( x, y ) {
    return x + y;
}
var v = add.toString();
// e.g., returns 'function add( x, y ) {\n    return x + y;\n}'

Notes

• In pre-ES2015 environments, only plain identifiers (without defaults) are valid JavaScript parameters.
• Creating Function objects with the Function constructor is less efficient than declaring a function via a function expression or a function statement.
• The Function constructor can be invoked without the new operator (using new and not using new both return a new Function object).
• The Function constructor creates functions which execute in the global scope. Hence, created functions cannot access variables local to the scope in which functions were created.

Examples

var Function = require( '@stdlib/function-ctor' );

var add = new Function( 'x', 'y', 'return x + y' );

var v = add( 1, 2 );
// returns 3

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Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.