Getting to the point

To get the point just run the provided snippet in firefox and then in chrome. In chrome the event.shiftKey will always return false.

Details

To implement the Ctrl / Alt / Shift detection, you can use the properties event.ctrlKey, event.altKey, and event.shiftKey in many event types.

This seems to work ok for Keyboard Events such as keydown / keypress / keyup.

For drag events though, there is a problem I managed to reproduce that happens ONLY in Safari browser (MAC OS).

I provide the script /snippet below. The problem is that, when I press Shift key while dragging the element, in all browsers the event.shiftKey gives "true" value. In Safari (tested on 14.01) this value is always false.

document.addEventListener("dragover", (event) => {
  var shiftKey = event.shiftKey;
  document.getElementById("div1").innerHTML = "<br>SHIFT pressed?  " + shiftKey;   
    }, false);

<div id="drag1"draggable="true">DRAG THIS TEXT WITH AND WITHOUT PRESSING SHIFT KEY<div>
<div id="div1"></div>