Support for JavaScript and JScript document and browser objects
Opera supports ECMAScript 2nd and 3rd edition fully, and intend to
support DOM level 2 fully (separate DOM documentation will be
forthcoming).
In practice Opera also supports JavaScript 1.4 with a few exceptions as
well as a subset of JScript. Opera only supports the JScript properties
when the user agent is set to Microsoft Internet Explorer. This you can do
through setting it to "Identify as MSIE 5.0" in Preferences >
Connections > Browser identification.