is it possible to check with my website if an app is installed?

var now = new Date().valueOf();
setTimeout(function () {
    if (new Date().valueOf() - now > 100) return;
    window.location = "https://itunes.apple.com/appdir";
}, 25);
window.location = "appname://";setTimeout(function () { window.location = "https://itunes.apple.com/appdir"; }, 25);
window.location = "appname://";