lpad

Left pad a string.

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 );