How to check if an app is installed from a web-page on an iPhone?

Question

I want to create a web-page, a page that will redirect an iPhone to the app-store if the iPhone does not have the application installed, but if the iPhone has the app instal

Answer 1

After compiling a few answers, I've come up with the following code. What surprised me was that the timer does not get frozen on a PC (Chrome, FF) or Android Chrome - the trigger worked in the background, and the visibility check was the only reliable info.

var timestamp             = new Date().getTime();
var timerDelay              = 5000;
var processingBuffer  = 2000;

var redirect = function(url) {
  //window.location = url;
  log('ts: ' + timestamp + '; redirecting to: ' + url);
}
var isPageHidden = function() {
    var browserSpecificProps = {hidden:1, mozHidden:1, msHidden:1, webkitHidden:1};
    for (var p in browserSpecificProps) {
        if(typeof document[p] !== "undefined"){
        return document[p];
      }
    }
    return false; // actually inconclusive, assuming not
}
var elapsedMoreTimeThanTimerSet = function(){
    var elapsed = new Date().getTime() - timestamp;
  log('elapsed: ' + elapsed);
  return timerDelay + processingBuffer < elapsed;
}
var redirectToFallbackIfBrowserStillActive = function() {
  var elapsedMore = elapsedMoreTimeThanTimerSet();
  log('hidden:' + isPageHidden() +'; time: '+ elapsedMore);
  if (isPageHidden() || elapsedMore) {
    log('not redirecting');
  }else{
    redirect('appStoreUrl');
  }
}
var log = function(msg){
    document.getElementById('log').innerHTML += msg + "
";
}

setTimeout(redirectToFallbackIfBrowserStillActive, timerDelay);
redirect('nativeApp://');

JS Fiddle