How to launch an iOS url-protocol-aware app via JS, but do something different if the app isn't installed

launchIOSAppFromJS.js

com.foo.MyApp.prototype.launchIOSAppOrITunesLink = function() {
    // Listen for the Safari window to be deactivated
    goog.events.listen(window, goog.events.EventType.BLUR, this.onMobileAppDetected, false, this);

    // Launch the mobile app protocol and *ALSO* launch a timer
    // that checks if the app was launched (it would have deactivated the mobile browser) 
    goog.Timer.callOnce(this.launchMobileApp, 100, this);
    goog.Timer.callOnce(this.checkAppState, 600, this);
};

com.foo.MyApp.prototype.onMobileAppDetected = function() {
    this.appDetected_ = true;
};

com.foo.MyApp.prototype.launchMobileApp = function() {
    // Change your URL to a an url-protocol that you know is
    // supported by your app:
    window.location.href = "myiosapp://";
    // Some other urls you can make:
    // myiosapp://
    // myiosapp://some/path/here
    // myiosapp://?foo=1&bar=2
    // myiosapp://some/path/here?foo=1&bar=2
};

com.foo.MyApp.prototype.checkAppState = function() {
    if (!this.appDetected_) {
        // We didn't deactivate immediately, so that app must not be installed
        // Launch iTunes link or show some messaging to the user
    } else {
        // App is launching, so not much to do here
    }
    // cleanup our deactivation listener
    goog.events.unlisten(window, goog.events.EventType.BLUR, this.onMobileAppDetected, false, this);
};

This is some code that was taken out of a google closure project, hence the goog.* calls