Jscript was the most evil of all the JS implementations. It's the reason why MOST of the thing people hate about JS are still in the language.

They wanted to remove a bunch of the badly-designed stuff from the language, but MicroSoft had just finished implementing Jscript complete with all those issues at great expense. They would rather have a language with issues than change their implementation, so the world got stuck with the issues and there's now too much code on the web to change without something drastic.

Mumbles about annoyances at hanging commas

I bet JSON would allow hanging commas if not for Jscript.