Q:

Why is this line of code necessary in clicking a button with JavaScript?

This solution was given to this question asking how to trigger an HTML button when Enter is pressed in an input field.
<input type="text" id="txtSearch" onkeypress="searchKeyPress(event);" />
<input type="button" id="btnSearch" Value="Search" onclick="doSomething();" />

<script>
function searchKeyPress(e)
{
    // look for window.event in case event isn't passed in
    if (typeof e == 'undefined' && window.event) { e = window.event; }
    if (e.keyCode == 13)
    {
        document.getElementById('btnSearch').click();
    }
}
</script>

Why is if (typeof e == 'undefined' && window.event) { e = window.event; } nescecary? It appears to be checking if the argument didn't get passed correctly, why wouldn't it? Is this related to fixing browser compatibility issues?

A:

Because old IE versions are a horrible abomination that use a global variable event instead of a function argument like any sane developer would use.
For the same reason (oldIE developers being insane) you cannot use .addEventListener() in oldIE but have to use .attachEvent() instead.
Edit: Just saw that you are using an inline event and always pass the event. That way you will always have a valid event object in the first argument of your function. You do not need the additional code.

