What is the difference between click in
document.getElementById(\"myBtn\").addEventListener(\"click\", displayDate);
and onclick in
The difference is that the first is an event listener, and the second is an event handler content attribute.
Event handler content attributes store an internal raw uncompiled handler, which produces an event listener via the event handler processing and getting the current value of the event handler algorithms.
In practice, this affects the scope, e.g.
(function() { var element = document.body;
var str = "console.log([typeof foo, typeof bar])";
var func = function() { console.log([typeof foo, typeof bar]); };
element.foo = 'foo';
var bar = 'bar';
element.setAttribute('onclick', str);
element.addEventListener('click', func);
element.click();
// Event handler content attribute logs ["string", "undefined"]
// Event listener logs ["undefined", "string"]
})();
I discourage using event handlers. They are an old reminiscence and are superseded by event listeners.