@stdlib/function-ctor/README.md

Function constructor.

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# Function

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> [Function][mdn-function] constructor.

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<section class="intro">

</section>

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<section class="installation">

## Installation

```bash
npm install @stdlib/function-ctor
```

</section>

<section class="usage">

## Usage

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

#### Function( \[...argNames,] body )

Returns a new [function][mdn-function] object.

```javascript
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).

* * *

### Properties

<a name="prop-length"></a>

#### Function.prototype.length

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

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

<a name="prop-name"></a>

#### Function.prototype.name

**Read-only** property representing the name of the function.

```javascript
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'
```

<a name="prop-prototype"></a>

#### Function.prototype.prototype

**Read-only** property representing the prototype of the function.

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

* * *

### Methods

<a name="method-apply"></a>

#### Function.prototype.apply( thisArg, args )

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

<!-- eslint-disable no-invalid-this -->

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

var ctx = {
    'initial': 10
};

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

<a name="method-bind"></a>

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

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

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

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

<a name="method-call"></a>

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

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

<!-- eslint-disable no-invalid-this -->

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

var ctx = {
    'initial': 10
};

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

<a name="method-to-string"></a>

#### Function.prototype.toString()

Returns a string representing the function.

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

</section>

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<section class="notes">

## 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.  

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

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

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

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

</section>

<!-- /.examples -->

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</section>

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<section class="related">

</section>

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2024. The Stdlib [Authors][stdlib-authors].

</section>

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[npm-image]: http://img.shields.io/npm/v/@stdlib/function-ctor.svg
[npm-url]: https://npmjs.org/package/@stdlib/function-ctor

[test-image]: https://github.com/stdlib-js/function-ctor/actions/workflows/test.yml/badge.svg?branch=v0.2.2
[test-url]: https://github.com/stdlib-js/function-ctor/actions/workflows/test.yml?query=branch:v0.2.2

[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/function-ctor/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/function-ctor?branch=main

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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/function-ctor/tree/deno
[deno-readme]: https://github.com/stdlib-js/function-ctor/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/function-ctor/tree/umd
[umd-readme]: https://github.com/stdlib-js/function-ctor/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/function-ctor/tree/esm
[esm-readme]: https://github.com/stdlib-js/function-ctor/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/function-ctor/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/function-ctor/main/LICENSE

[mdn-function]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function

</section>

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