jQuery: Change meta title tag when page is not being viewed

new_gist_file.js

//Code found here: https://graphicfusion.design/

jQuery(document).ready(function($) {

    (function() {
        var hidden = "hidden";
        var oldtitle = document.title;
        var currenttitle;
        if (hidden in document)
            document.addEventListener("visibilitychange", onchange);
        else if ((hidden = "mozHidden") in document)
            document.addEventListener("mozvisibilitychange", onchange);
        else if ((hidden = "webkitHidden") in document)
            document.addEventListener("webkitvisibilitychange", onchange);
        else if ((hidden = "msHidden") in document)
            document.addEventListener("msvisibilitychange", onchange);
        else if ("onfocusin" in document)
            document.onfocusin = document.onfocusout = onchange;
        else
            window.onpageshow = window.onpagehide = window.onfocus = window.onblur = onchange;
        function onchange(evt) {
            var v = "visible"
              , h = "hidden"
              , evtMap = {
                focus: v,
                focusin: v,
                pageshow: v,
                blur: h,
                focusout: h,
                pagehide: h
            };
            evt = evt || window.event;
            if (evt.type in evtMap) {
                currenttitle = oldtitle;
                $(document).attr('title', currenttitle);
            } 
            else {
                currenttitle = this[hidden] ? "Miss You ︎:( " : oldtitle;
                $(document).attr('title', currenttitle);
            }
        }
        if (document[hidden] !== undefined)
            onchange({
                type: document[hidden] ? "blur" : "focus"
            });
    }
    )();
}
);