JS isRetina()

isRetina.js

isRetina = function(){
    var mediaQuery = '(-webkit-min-device-pixel-ratio: 1.5), (min--moz-device-pixel-ratio: 1.5), (-o-min-device-pixel-ratio: 3/2), (min-resolution: 1.5dppx)';
    var root = (typeof exports === 'undefined' ? window : exports);
    if (root.devicePixelRatio > 1) {
        return true;
    }

    if (root.matchMedia && root.matchMedia(mediaQuery).matches) {
        return true;
    }

    return false;
};