is there a way to re-trigger video dialog in browser?

Question

Lets say user has blocked access to camera and if I check it like this:

navigator.mediaDevices.getUserMedia({ audio: false, video: true })
  .then(function(stream) {
    // do something
  })
  .catch(function(err) {
    console.log(err)
  });

The exception is thrown as the camera is not allowed.

Answer 1

No not really. If so then sites would just keep asking for it which would annoy the user endlessly.

If the user denies this you'll have to show a message in your application that tells the user to go and enable it in their browser (which is a bit different for each browser).