How do I prevent a browser page refresh in JavaScript?

Question

I would like to prevent an HTML page refresh (given a variable refreshMode != 1):

window.onbeforeunload = function(e) {
   if(refreshMode == 1){
     return;
   }else{
     // don't do it!
    e.preventDefault();
   }
};

I have tried e.preventDefault() and e.stopPropagation(), but neither appears to be preventing the refresh from submit the request.

Is it possible to do this?

Answer 1

Set a return value in additiont o preventing default. You cannot change the prompt text (that used to be possible), and you cannot prevent the prefresh if the user confirms on the prompt.

See https://developer.mozilla.org/en-US/docs/Web/API/Window/beforeunload_event

window.addEventListener('beforeunload', (event) => {
  // Cancel the event as stated by the standard.
  event.preventDefault();
  // Chrome requires returnValue to be set.
  event.returnValue = '';
});