Java-based interpreter for JavaScript

Question

As a project in school i have to make a JavaScript interpreter. (Everything incl. the entire backend has to be made by me).

Everything has to be written in Java - i use ANTLR for parsing and generating ASTs.

currently i can parse some .js code into an AST - and therefore need to translate this AST into som kind of intermediate-representation that can be executed on a bytecode machine.

I have some experience writing compilers for statically typed languages, but im very much in doubt how to proceed from here since JS is a dynamically typed language.

If you can give me some good advices on how to proceed i would be gratefull!

Personally i think i have to make the bytecode-machine first and then make the IR fit this machine afterwards. Unfortunatly i cant really find any good tutorials on how to write a bytecode-machine.

PS. im familiar with following books on the topic :

"modern compiler implementation in Java (Appel)", "Programming language processors in Java (Watt & Brown)", "Language implementation patterns (Parr)"

Regards Sune

Answer 1

If you only want to execute the javascript you do not need to transform the AST into IR and then into (some?) bytecode that would also force you to do a bytecode executer.

Why not just execute the javascript AST in a java "engine"? You can store all values as a Map<String, Object> and interpret them as you walk the AST. A new function get an environment/context (a new Map<...>).

If you cannot find a value in the current context you will have to fall back on the global context (=Map).

For the "dynamic" behaviour: If you need an double for an addition you only parse the Object.toString() value to an double using the standard way (more dynamic than that is hard to get :) ):

String value = contextMap.get(key); 
Double dvalue = Double.parseDouble(value.toString());
....