Set RGB brightness

HTML

<div id="origin_color" style="width:100px; height:100px">Origin Color</div>
<div id="converted_color" style="width:100px; height:100px">Converted Color</div>
Input Color(e.g. #ff0000): <input type="text" id="input_color"></input><br>
Brightness(0~100): <input type="text" id="input_brightness"></input><br>
Output Color: <div id="output_color"></div>
Original brightness: <div id="original_brightness"></div>
<br>
<div id="button">Click here to convert!!</div>

<div id="origin_color2" style="width:100px; height:100px">Origin Color</div>
<div id="converted_color2" style="width:100px; height:100px">Converted Color</div>

JavaScript

$(function(){
    $('#button').click(function(){
    var inputColor = $('#input_color').val(),
        inputBrightness = $('#input_brightness').val(),
        outputColor = getNewBrightnessColor(inputColor, inputBrightness);

    $('#output_color').text(outputColor);
    $('#origin_color').css('background-color', inputColor);
    $('#converted_color').css('background-color', outputColor);
    });
});

function getNewBrightnessColor(rgbcode, brightness) {
    var r = parseInt(rgbcode.slice(1, 3), 16),
        g = parseInt(rgbcode.slice(3, 5), 16),
        b = parseInt(rgbcode.slice(5, 7), 16),
        HSL = rgbToHsl(r, g, b),
        RGB;
        
    $('#original_brightness').text(HSL[2] * 100);
    
    RGB = hslToRgb(HSL[0], HSL[1], brightness / 100);
    rgbcode = '#'
        + convertToTwoDigitHexCodeFromDecimal(RGB[0])
        + convertToTwoDigitHexCodeFromDecimal(RGB[1])
        + convertToTwoDigitHexCodeFromDecimal(RGB[2]);
    
    return rgbcode;
}

function convertToTwoDigitHexCodeFromDecimal(decimal){
    var code = Math.round(decimal).toString(16);
    
    (code.length > 1) || (code = '0' + code);
    return code;
}
/**
 * Converts an RGB color value to HSL. Conversion formula
 * adapted from http://en.wikipedia.org/wiki/HSL_color_space.
 * Assumes r, g, and b are contained in the set [0, 255] and
 * returns h, s, and l in the set [0, 1].
 *
 * @param   Number  r       The red color value
 * @param   Number  g       The green color value
 * @param   Number  b       The blue color value
 * @return  Array           The HSL representation
 */
function rgbToHsl(r, g, b){
    r /= 255, g /= 255, b /= 255;
    var max = Math.max(r, g, b), min = Math.min(r, g, b);
    var h, s, l = (max + min) / 2;

    if(max == min){
        h = s = 0; // achromatic
    }else{
        var d = max - min;
        s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
        switch(max){
            case r: h = (g - b) / d + (g < b ? 6 : 0); break;
            case g: h = (b...