@stdlib/string-base-left-pad

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

Left pad a string.

Installation

npm install @stdlib/string-base-left-pad

Usage

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.

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

  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 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 truncation behavior

  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

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: right pad a string.

---

Notice

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

Community

---

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.