Well, actually the IE implementation is called JScript, JavaScript(TM) is the implementation of Mozilla.
JScript and JavaScript are two ECMAScript-based dialects.
JavaScript 1.5 conforms with the ECMAScript 3rd Edition Standard, the subsequent versions, JS 1.6, 1.7 and 1.8 introduce language features that are out of that standard edition, often called Mozilla Extensions.
That’s why JScript doesn’t have any of these features, because they are not part of the ECMA Standard.