npm package: @stdlib/string-left-pad
Description: Left pad a string.
Author: The Stdlib Authors
Latest version: 0.2.3

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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>

# lpad

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

> Left pad a string.

<section class="installation">

## Installation

```bash
npm install @stdlib/string-left-pad
```

</section>

<section class="usage">

## Usage

```javascript
var lpad = require( '@stdlib/string-left-pad' );
```

#### lpad( str, len\[, pad] )

Left pads a string such that the padded string has a length of **at least** `len`.

```javascript
var str = lpad( 'a', 5 );
// returns '    a'
```

By default, an input string is padded with a Unicode "space" character (U+0020). To pad with a different character or sequence of characters, provide a `pad` string.

```javascript
var str = lpad( 'beep', 10, 'b' );
// returns 'bbbbbbbeep'

str = lpad( 'boop', 12, 'beep' );
// returns 'beepbeepboop'
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   An output string is **not** guaranteed to have a length of **exactly** `len`, but to have a length of **at least** `len`. To generate a padded string having a length equal to `len`

    ```javascript
    var str = lpad( 'boop', 10, 'beep' ); // => length 12
    // returns 'beepbeepboop'

    str = str.substring( str.length-10 ); // => length 10
    // returns 'epbeepboop'
    ```

-   This function differs from [`String.prototype.padStart`][mdn-string-padstart] in the following ways:

    -   The function is **not** guaranteed to return a string having a length exactly equal to `len` (as explained above).
    -   The function does **not** truncate `pad` (from the end) in order to ensure the returned string has length `len`.

    To replicate [`String.prototype.padStart`][mdn-string-padstart] truncation behavior

    ```javascript
    var floorb = require( '@stdlib/math-base-special-floorb' );

    function padStart( str, len, pad ) {
        var n;
        if ( len <= str.length ) {
            return str;
        }
        n = floorb( len-str.length, 1, pad.length ) + str.length;
        return pad.substring( 0, len-n ) + lpad( str, n, pad );
    }

    var str = padStart( 'boop', 10, 'beep' );
    // returns 'bebeepboop'
    ```

</section>

<!-- /.notes -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random-base-discrete-uniform' );
var lpad = require( '@stdlib/string-left-pad' );

var str = 'beep';
var i;
for ( i = 0; i < 100; i++ ) {
    console.log( lpad( str, discreteUniform( str.length, str.length+10 ), 'b' ) );
}
```

</section>

<!-- /.examples -->



<!-- 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/string-left-pad-cli`][@stdlib/string-left-pad-cli]</span><span class="delimiter">: </span><span class="description">CLI package for use as a command-line utility.</span>
-   <span class="package-name">[`@stdlib/string-pad`][@stdlib/string/pad]</span><span class="delimiter">: </span><span class="description">pad a string.</span>
-   <span class="package-name">[`@stdlib/string-right-pad`][@stdlib/string/right-pad]</span><span class="delimiter">: </span><span class="description">right pad a string.</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 -->

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

<section class="links">

[@stdlib/string-left-pad-cli]: https://www.npmjs.com/package/@stdlib/string-left-pad-cli

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

[test-image]: https://github.com/stdlib-js/string-left-pad/actions/workflows/test.yml/badge.svg?branch=v0.2.3
[test-url]: https://github.com/stdlib-js/string-left-pad/actions/workflows/test.yml?query=branch:v0.2.3

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

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

[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors

[cli-section]: https://github.com/stdlib-js/string-left-pad#cli
[cli-url]: https://github.com/stdlib-js/string-left-pad/tree/cli
[@stdlib/string-left-pad]: https://github.com/stdlib-js/string-left-pad/tree/main

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

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/string-left-pad/main/LICENSE

[standard-streams]: https://en.wikipedia.org/wiki/Standard_streams

[mdn-regexp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions

[mdn-string-padstart]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart

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

[@stdlib/string/pad]: https://www.npmjs.com/package/@stdlib/string-pad

[@stdlib/string/right-pad]: https://www.npmjs.com/package/@stdlib/string-right-pad

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

</section>

<!-- /.links -->