CustomURL: Launch app if app is installed, else open an alternate URL (Android all browsers)

gistfile1.js

<script type="text/javascript">
    var custom = "myapp://custom_url";
    var alt = "http://mywebsite.com/alternate/content";
    var g_intent = "intent://scan/#Intent;scheme=zxing;package=com.google.zxing.client.android;end";
    var timer;
    var heartbeat;
    var iframe_timer;

    function clearTimers() {
        clearTimeout(timer);
        clearTimeout(heartbeat);
        clearTimeout(iframe_timer);
    }

    function intervalHeartbeat() {
        if (document.webkitHidden || document.hidden) {
            clearTimers();
        }
    }

    function tryIframeApproach() {
        var iframe = document.createElement("iframe");
        iframe.style.border = "none";
        iframe.style.width = "1px";
        iframe.style.height = "1px";
        iframe.onload = function () {
            document.location = alt;
        };
        iframe.src = custom;
        document.body.appendChild(iframe);
    }

    function tryWebkitApproach() {
        document.location = custom;
        timer = setTimeout(function () {
            document.location = alt;
        }, 2500);
    }

    function useIntent() {
        document.location = g_intent;
    }

    function launch_app_or_alt_url(el) {
        heartbeat = setInterval(intervalHeartbeat, 200);
        if (navigator.userAgent.match(/Chrome/)) {
            useIntent();
        } else if (navigator.userAgent.match(/Firefox/)) {
            tryWebkitApproach();
            iframe_timer = setTimeout(function () {
                tryIframeApproach();
            }, 1500);
        } else {
            tryIframeApproach();
        }
    }

    $(".source_url").click(function (event) {
        launch_app_or_alt_url($(this));
        event.preventDefault();
    });
</script>