Question

function doSomething(e) {
    var targ;
    if (!e) var e = window.event; //<<<< what does it do this check?
    if (e.target) targ = e.target;
}

Why do we need to check this?

Answer 1

This adds compatibility with older (Internet Explorer?) browsers that didn’t support passing the event object to handlers but instead defined them on the window object.

Also the var is not needed in var e = window.event because it’s already declared (parameter).

It can also be written as e = e || window.event;