myjs

A JavaScript interpreter for Python. It runs a practical subset of ECMAScript against a server-side DOM, hands scripts an ffi bridge to native C libraries, and lets JavaScript reach the entire Python ecosystem.

pip install myjs

myjs                 # start a REPL
myjs script.js       # execute a file
myjs -e "6 * 7"      # evaluate a snippet
myjs --gui app.js    # run, then show the DOM the script built in a native window

import myjs

myjs.eval("1 + 2 * 3")            # -> 7
myjs.run("script.js")

s = myjs.Session()                # an isolated global scope
s.eval("const x = 21;")
s.eval("x * 2")                   # -> 42

What a script can reach

• The DOM — document, window, and ~190 constructors (URL, Headers, Event, DOMRect, …). document.createElement(...).appendChild(...) builds a real object tree.

• An event loop — Promise (with all / allSettled / race / any), async / await, setTimeout / setInterval, queueMicrotask. Microtasks run before timers.

• ES modules — import / export from .js files; a bare specifier resolves to a Python module.

• ffi — call native C libraries through ctypes, no compiler:

  const libc = ffi.loadLibrary("c");
  libc.abs.argtypes = [ffi.types.int];
  libc.abs.restype  = ffi.types.int;
  libc.abs(-42);                       // 42
  

• Host bindings — fs, path, sh (shell), http + an async fetch, os (Node-flavoured), process, WebSocket (a real RFC 6455 client), say / notify / open, hash, atob / btoa.

• py — py.import("numpy"), py.eval(...), py.list(iter) → the whole Python package index from JavaScript.

The language layer passes a curated test262-style battery: closures, classes (extends / super / fields / getters-setters / private / static), destructuring, generators, labelled break, async / await, and the Array / String / Object / Number / Math / JSON / RegExp built-ins. Not covered: real prototype chains, Proxy / Symbol, with.

Language embedding

s = myjs.Session(scope={"answer": 42})
s.eval("answer * 2")              # -> 84

A JavaScript exception that escapes becomes myjs.JSError with js_name, js_line, and js_trace (the call stack).

How it is built

myjs is the runtime layer on top of the domonic-libs acorn port — a faithful Python port of the acorn parser plus a tree-walking evaluator — which in turn runs on domonic's DOM. Full reference: docs/myjs.md.

MIT licensed.