After making some research, I now know that I can launch an iphone app by scanning a QR code.
Instead of generating the QR code for the app’s custom url, I want to have dedicated html page where it will decide weather to lunch the app if it existes or to redirect to another url like itunes download page etc. but now from Javascript how we can make this decision?
And the whole thing should happen automatically not on click like the solution given on this link.
I once seen the same exact solution I am looking for when I scan a QR code on VEVO youtube page.
it looks there is no solution for this unless iOS safari give some handle where developers can make use of when a url is invalid (the app does not exist).
so far user will see the error message from safar for some time before it is redirected to apostle or some other page.