User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_1) AppleWebKit/537.1 (KHTML, like Gecko) Chrome/21.0.1180.89 Safari/537.1 Steps to reproduce: Because no directive flags, we cannot recognize this expression statement is directive or not. Actual results: For example, function t() { ("use strict"); } in this script, "use strict" is not directive. But we have no way to distinguish from function t() { "use strict"; } in Mozilla Parser API AST. Expected results: I suggest that adding directive flag to ExpressionStatement or introducing new statement type, DirectiveStatement.

+1 new statement type, `DirectiveStatement`.

I've opened the same issue to esprima. http://code.google.com/p/esprima/issues/detail?id=330

Either solution would work. If we want to be pedantic about compatibility, directive flag is better since it does not change the syntax node.

If I were really looking for true ASTs, I'd expect the () to be visible in the AST, which would let you distinguish the ("use strict") case. But there's also "use\<newline>strict" and "use stri\ct" and "us<escape encoding e> strict" and so on, so a directive annotation of some sort does seem right to me. Best ideally might be having the directive prolog as the left arm of a binary with the right as the actual source statements, but given the existing setup, DirectiveStatement seems right to me.