@stdlib/string/base/left-pad/README.md

String manipulation functions.

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# lpad

> Left pad a string.

<section class="usage">

## 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'
```

</section>

<!-- /.usage -->

<section class="notes">

## 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'
    ```

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```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 );
```

</section>

<!-- /.examples -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/string/base/right-pad`][@stdlib/string/base/right-pad]</span><span class="delimiter">: </span><span class="description">right pad a string.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="links">

[mdn-string-padstart]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart

<!-- <related-links> -->

[@stdlib/string/base/right-pad]: https://github.com/stdlib-js/string/tree/main/base/right-pad

<!-- </related-links> -->

</section>

<!-- /.links -->