Left pad a string.
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> Left pad a string.
``bash`
npm install @stdlib/string-left-pad
`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'
`
- 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).pad
- The function does not truncate (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'
`
`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' ) );
}
`
- [@stdlib/string-left-pad-cli][@stdlib/string-left-pad-cli]: CLI package for use as a command-line utility.
- [@stdlib/string-pad][@stdlib/string/pad]: pad a string.
- [@stdlib/string-right-pad][@stdlib/string/right-pad]: right pad a string.
*
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
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---
See [LICENSE][stdlib-license].
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
[@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
[chat-image]: https://img.shields.io/badge/zulip-join_chat-brightgreen.svg
[chat-url]: https://stdlib.zulipchat.com
[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
[@stdlib/string/pad]: https://www.npmjs.com/package/@stdlib/string-pad
[@stdlib/string/right-pad]: https://www.npmjs.com/package/@stdlib/string-right-pad