JavaScript variables set in onclick - different behaviour in IE / FF

I recently discovered that the behaviour of internet explorer and Firefox is quite different when it comes to settings variables in an onClick event - in Firefox these variables will become global variables, in IE they are just "local" and will nur be available for other functions.

An example:

a onClick="variableA = 'peter';CallFunction();return false;" ...

function CallFunction() {
alert(variableA);
}

In FF, an alert box will show "Peter", in IE you'll receive an exception.

How to solve that? Simply declare variableA on top of your JavaScript file, this way IE will modify the global variable.

var variableA = '';