Assigning Same Onclick Dynamically And Statically

I have a function whose parameter is a reference the element that called it:

function someFunction(el)
{
...
}

The function is assigned to the onclick event of some elements in the
HTML source:

<input ... onclick="someFunction(this);" ...>

and dynamically to others:

elRef.onclick = someFunction;

When someFunction() is called from the statically-assigned onclick, el
is a reference to the element. But when it has been added dynamically,
el will be either undefined (IE) or 'event' (Mozilla et al).

To assign the right value to el, I can test if el exists and if it does,
whether its constructor is some type of HTML element or 'Event'. But IE
doesn't support the constructor property for elements (or have I just
not found it yet?) nor does it understand 'Event' the way Mozilla does. Code: