For somebody facing the same issue at this day and age (been 9 years since the question was asked), JScript has a builtin Array.prototype.at() that serves that exact purpose, so, from the OP's code:

For i = 0 To myArray.length - 1
    Response.Write(myArray.at(i))
Next

Without any need for extra-do's. I think this should have worked back when the question was asked as I believe the implementation hasn't changed ECMA edition since then.

For what Microsoft claims, JScript is an implementation of ECMAScript3 (web archive), so hopefully anything in MDN that claims to be ECMAScript3 compatible should work in JScript and even nowadays MDN is a great (and up-to-date!) reference for JScript syntax.

Maybe the very best, maintained, and specific documentation for ECMAScript edition 3, or ECMA-262 is available at https://tc39.es/ecma262/