npm package: @stdlib/object-for-in
Description: Invoke a function for each own and inherited enumerable property of an object.
Author: The Stdlib Authors
Latest version: 0.1.1

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<details>
  <summary>
    About stdlib...
  </summary>
  <p>We believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js.</p>
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</details>

# forIn

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

> Invoke a function for each own and inherited enumerable property of an object.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/object-for-in
```

</section>

<section class="usage">

## Usage

```javascript
var forIn = require( '@stdlib/object-for-in' );
```

#### forIn( obj, fcn\[, thisArg ] )

Invokes a `function` for each own and inherited enumerable property of an `object`.

```javascript
function log( value, key ) {
    console.log( '%s: %d', key, value );
}

function Foo() {
    this.a = 1;
    this.b = 2;
    return this;
}

Foo.prototype.c = 3;
Foo.prototype.d = 4;

var obj = new Foo();

forIn( obj, log );
/* e.g., =>
    a: 1
    b: 2
    c: 3
    d: 4
*/
```

The invoked `function` is provided three arguments:

-   **value**: object property value.
-   **key**: object property.
-   **obj**: the input object.

To terminate iteration before visiting all properties, the provided function must explicitly return `false`.

```javascript
function log( value, key ) {
    console.log( '%s: %d', key, value );
    return false;
}

var obj = {
    'a': 1,
    'b': 2,
    'c': 3,
    'd': 4
};

forIn( obj, log );
// e.g., => a: 1
```

To set the function execution context, provide a `thisArg`.

```javascript
function sum( value ) {
    this.sum += value;
    this.count += 1;
}

var obj = {
    'a': 1,
    'b': 2,
    'c': 3,
    'd': 4
};

var context = {
    'sum': 0,
    'count': 0
};

forIn( obj, sum, context );

var mean = context.sum / context.count;
// returns 2.5
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   The function returns the input `object`.
-   Property iteration order is **not** guaranteed.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var fromCodePoint = require( '@stdlib/string-from-code-point' );
var forIn = require( '@stdlib/object-for-in' );

function update( value, key, obj ) {
    console.log( '%s: %d', key, value );
    obj[ key ] *= value;
}

function Foo() {
    return this;
}

Foo.prototype.beep = 3.14;

var obj;
var key;
var i;

obj = new Foo();
for ( i = 0; i < 26; i++ ) {
    key = fromCodePoint( 97 + i );
    obj[ key ] = i;
}

forIn( obj, update );
console.log( obj );
```

</section>

<!-- /.examples -->

<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="references">

</section>

<!-- /.references -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/utils-for-each`][@stdlib/utils/for-each]</span><span class="delimiter">: </span><span class="description">invoke a function for each element in a collection.</span>
-   <span class="package-name">[`@stdlib/object-for-own`][@stdlib/object/for-own]</span><span class="delimiter">: </span><span class="description">invoke a function for each own enumerable property of an object.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->


<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; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

<!-- /.stdlib -->

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[npm-url]: https://npmjs.org/package/@stdlib/object-for-in

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[test-url]: https://github.com/stdlib-js/object-for-in/actions/workflows/test.yml?query=branch:v0.1.1

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

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[stdlib]: https://github.com/stdlib-js/stdlib

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

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/object-for-in/main/LICENSE

<!-- <related-links> -->

[@stdlib/utils/for-each]: https://www.npmjs.com/package/@stdlib/utils-for-each

[@stdlib/object/for-own]: https://www.npmjs.com/package/@stdlib/object-for-own

<!-- </related-links> -->

</section>

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