In this SO question, I took a look at the JavaScript runtime to see if buildParseTrees is defined for a parser. Indeed it is, but I noticed there is one applied occurrence of the field erroneously spelled _buildParseTrees. Of course, in the warped world of JS, this is not caught either by compiler or runtime.

Also, there is no "getBuildParseTree()" noted here and here.

I realize "code reviews" are old school, but relying on a terrible programming language like Javascript to find errors is not going to work.