dpr.js

(function () {

    // set default ratio value
    let ratio = 1;

    // use systemXDPI and logicalXDPI if available
    if (window.screen.systemXDPI !== undefined
        && window.screen.logicalXDPI !== undefined
        && window.screen.systemXDPI > window.screen.logicalXDPI) {

        ratio = window.screen.systemXDPI / window.screen.logicalXDPI;
    }

    // use devicePixelRatio if available
    else if (window.devicePixelRatio !== undefined) {
        ratio = window.devicePixelRatio;
    }

    if (typeof define === 'function' && define.amd) {
        define(ratio.toFixed(1));
    } else {
        window.DPR = ratio.toFixed(1);
    }

})();