Checking for NULL value?

Copied from jane003 a couple of messages down...

editor_frame = document.getElementById(instanceName+'___Frame');
if(editor_frame == null)
{
alert("You know what? The editor frame is NULL!!");
}

In a function is where it goes. Like so:

function checkIfNull(instanceName) {
editor_frame = document.getElementById(instanceName+'___Frame');
if(editor_frame == null)
{
alert("You know what? The editor frame is NULL!!");
}
}

then have a button <input type="button" onclick="javascript:checkIfNull('theInstanceNameGoesHere');">

Theoretically...