Project set up following Javascript Setup section of the ANTLR Mega Tutorial. Reference to original repo at: https://github.com/unosviluppatore/antlr-mega-tutorial.
Use yarn install to install antlr4 dependency.
It should also invoke postinstall script that generates parser and lexer from grammar;
make sure that antlr4 executable is available in path.
If not, parser and lexer can be easily generated using yarn antlr or:
antlr4 -Dlanguage=JavaScript -o gen/ src/Chat.g4