Why Does The Event Handler Throws An Error In Firefox?

The following snippet works fine in the Google Chrome browser, but if I run it in Firefox it throws an error saying event is not defined. What causes this problem?

Solution 1:

The global variable event is non-standard and Firefox does not support it.

Access the event object through the standard method (the first argument to the event handler) instead.

document.getElementById("btn").addEventListener("click", function(event) {
  console.log(event.target.id)
});

<inputtype="button"id="btn"value="Click Me">