contrast-color.js

/**
 * Calculate the contrast of a color to determine the appropriate opposing text color.
 * @author  D. Condrey
 * @param  {string|object} - element background-color or element
 * @return {string}
 *   white - if background is a dark shade color
 *   black - if background is a light shade color
 */
define(function() {

    'use strict';

    var colors = {};

    colors.contrast = function(rgb) {
        // check if we are receiving an element or element background-color
        if (rgb instanceof jQuery) {
            // get element background-color
            rgb = rgb.css('background-color');
        } else if (typeof rgb !== 'string') {
            return;
        }

        // @TODO check for HEX value
        // All browsers should return an rgb value so this isn't critical

        // Strip everything except the integers eg. "rgb(" and ")" and " "
        rgb = rgb.split(/\(([^)]+)\)/)[1].replace(/ /g, '');

        // map RGB values to variables
        var r = parseInt(rgb.split(',')[0], 10),
            g = parseInt(rgb.split(',')[1], 10),
            b = parseInt(rgb.split(',')[2], 10),
            a;

        // if RGBA, map alpha to variable (not currently in use)
        if (rgb.split(',')[3] !== null) {
            a = parseInt(rgb.split(',')[3], 10);
        }

        // calculate contrast of color (standard grayscale algorithmic formula)
        var contrast = (Math.round(r * 299) + Math.round(g * 587) + Math.round(b * 114)) / 1000;

        return (contrast >= 128) ? 'black' : 'white';
    };

    // Return public interface
    return colors;
});

...could do. Could do.

Or... yanno...

function contrastingColor(hex, factorAlpha=false) {
    let [r,g,b,a]=hex.replace(/^#?(?:(?:(..)(..)(..)(..)?)|(?:(.)(.)(.)(.)?))$/, '$1$5$5$2$6$6$3$7$7$4$8$8').match(/(..)/g).map(rgb=>parseInt('0x'+rgb));
    return ((~~(r*299) + ~~(g*587) + ~~(b*114))/1000) >= 128 || (!!(~(128/a) + 1) && factorAlpha) ? '#000' : '#FFF';   
}

...which takes any form of HEX or HEXA color code (#RGB/#RGBA/#RRGGBB/#RRGGBBAA; "#" is optional), along with a second param telling it if it should factor opacity.

Returns #FFF or #000.

It's a utility function!

@NerdyDeedsLLC looks like some kind of Trojan horse kind of snippet.