@stdlib/string-left-pad

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lpad

Left pad a string.

Installation

npm install @stdlib/string-left-pad

Usage

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.

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.

var 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( 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-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' ) );
}

See Also

• @stdlib/string-left-pad-cli: CLI package for use as a command-line utility.
• @stdlib/string-pad: pad a string.
• @stdlib/string-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.