Subj : Array and [ ]
To   : netscape.public.mozilla.jseng
From : Igor Bukanov
Date : Fri Jan 21 2005 11:49 pm

Hi!

Consider the following JS:

function Array()
{
     if (typeof alert == "function")
	alert("Intercepted");
     else
	print("Intercepted");
}

var x = [];


In SpiderMonkey and Rhino it prints "Intercepted", while in MS JScript 
it prints nothing, that is AFAICS in MS JScript [] always uses original 
Array constructor while SM and Rhino literally follows 11.1.4 in 
ECMAScript standard which states:

The production ArrayLiteral : [ Elision opt ] is evaluated as follows:
1. Create a new array as if by the expression "new Array()"
....

Clearly MS JScript violates this (although I can imagine that "as if by 
the expression" can be interpreted in a way that allows MS JScript 
implementation). But this is a useful violation since I spend some time 
trying to figure out why a script did not work properly only to find out 
that [] was called inside "with (objectWithArrayProperty)".

So the question is was this ability to change [] semantics via Array 
modification intentional?

Regards, Igor

.