https://github.com/stdlib-js/string-base-left-pad
Left pad a string.
https://github.com/stdlib-js/string-base-left-pad
base javascript left lpad node node-js nodejs pad padding stdlib str string util utilities utility utils
Last synced: 9 months ago
JSON representation
Left pad a string.
- Host: GitHub
- URL: https://github.com/stdlib-js/string-base-left-pad
- Owner: stdlib-js
- License: apache-2.0
- Created: 2022-09-08T00:10:28.000Z (over 3 years ago)
- Default Branch: main
- Last Pushed: 2025-03-10T02:35:55.000Z (11 months ago)
- Last Synced: 2025-05-07T11:56:58.838Z (9 months ago)
- Topics: base, javascript, left, lpad, node, node-js, nodejs, pad, padding, stdlib, str, string, util, utilities, utility, utils
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 347 KB
- Stars: 2
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
Awesome Lists containing this project
README
About stdlib...
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.
The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases.
When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there.
To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!
# lpad
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> Left pad a string.
## Installation
```bash
npm install @stdlib/string-base-left-pad
```
Alternatively,
- To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).
The [branches.md][branches-url] 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
```javascript
var lpad = require( '@stdlib/string-base-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'
str = lpad( 'beep', 10, 'b' );
// returns 'bbbbbbbeep'
str = lpad( 'boop', 12, 'beep' );
// returns 'beepbeepboop'
```
## 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( 0, 10 ); // => length 10
// returns 'beepbeepbo'
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'
```
## Examples
```javascript
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var papply = require( '@stdlib/utils-papply' );
var papplyRight = require( '@stdlib/utils-papply-right' );
var naryFunction = require( '@stdlib/utils-nary-function' );
var map = require( '@stdlib/utils-map' );
var logEach = require( '@stdlib/console-log-each' );
var lpad = require( '@stdlib/string-base-left-pad' );
// Define a string to pad:
var str = 'beep';
// Generate random lengths:
var lens = discreteUniform( 10, str.length, str.length+10 );
// Create a function for creating padded strings:
var fcn = naryFunction( papply( papplyRight( lpad, 'b' ), str ), 1 );
// Generate padded strings:
var out = map( lens, fcn );
// Print results:
logEach( '%s', out );
```
* * *
## See Also
- [`@stdlib/string-base/right-pad`][@stdlib/string/base/right-pad]: right pad a string.
* * *
## 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 © 2016-2025. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/string-base-left-pad.svg
[npm-url]: https://npmjs.org/package/@stdlib/string-base-left-pad
[test-image]: https://github.com/stdlib-js/string-base-left-pad/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/string-base-left-pad/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/string-base-left-pad/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/string-base-left-pad?branch=main
[chat-image]: https://img.shields.io/gitter/room/stdlib-js/stdlib.svg
[chat-url]: https://app.gitter.im/#/room/#stdlib-js_stdlib:gitter.im
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[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-base-left-pad/tree/deno
[deno-readme]: https://github.com/stdlib-js/string-base-left-pad/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/string-base-left-pad/tree/umd
[umd-readme]: https://github.com/stdlib-js/string-base-left-pad/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/string-base-left-pad/tree/esm
[esm-readme]: https://github.com/stdlib-js/string-base-left-pad/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/string-base-left-pad/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/string-base-left-pad/main/LICENSE
[mdn-string-padstart]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart
[@stdlib/string/base/right-pad]: https://github.com/stdlib-js/string-base-right-pad