Is there a tool to validate ECMAScript and confirm it is compatible with ECMAScript Language Specification 3rd edition?

You can use Esprima for this.

"ECMAScript parsing infrastructure for multipurpose analysis"

If you feed your last chunk to Esprima's validator, it says that "Code is syntatically valid."

Esprima follows ES5, so technically it could pass ES5-related syntax which ES3-only-compliant parser will not understand.

But in this case I don't see anything related to ES5, so it must be a bug in JSDT.