Check if app installed and redirect to download.

gistfile1.txt

function startiThrown() {
    document.location = appurl;
    var time = (new Date()).getTime();
    setTimeout(function(){
        var now = (new Date()).getTime();

        if((now-time)<400) {
            if(confirm('You do not seem to have iThrown installed, do you want to go download it now?')){
            document.location = 'http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=293049283&mt=8&uo=6';
            }
         }
    }, 300);
}