Maxime can you check if there isn't a problem with declarations of the form: var foo; which should be equivalent to var foo = undefined; The code generated for insertErrorIR is currently wrong, but when I make a small modification to the function, like this: function insertErrorIR(context, errorName, errorMsg) { // Find the error contructor var errorCtor = undefined; //FIXME: was just: var errorCtor; switch (errorName) { case 'RangeError': the function works properly. In other words, the absence of an initializer does not behave like an "undefined" explicit initializer. Marc