As a follow up in case anyone is curious about the why behind this assertion, consider a line of code like this

    eval("myObject."+functionName+"()")

Not only does it make it difficult to track down the calls to this method, it is now impossible to minify this chunk of code, something that is very commonly done in javascript. This is why javascript includes things like apply() and accessing members of an object in multiple ways (obj.attribute == obj['attribute'], for user-defined values of attribute).