Interactive JS

Interactive JS is a (very) simplified implementation of a JavaScript engine in JavaScript. It runs a script in a sandboxed environment, and allows users to register actions at any step.

It relies on esprima for syntactic analysis, and then proceeds to step asynchronously through the Abstract Syntax Tree (AST), keeping track of executions contexts and scope chains.

Usage

const Engine = require("./engine.js");

var script = `
function foo(a=1) {
  console.log(a);
}

foo(2);
`;
var e = Object.create(Engine);
e.addAction("CallExpression", function(e) {console.log("pre call: ", e.type);}, "before");
e.addAction("CallExpression", function(e) {console.log("post call: ", e.type);}, "after");
e.addAction(/.*/, function(n) {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      console.log(n.type);
      resolve();
    }, 50);
  });
}, "before");

e.run(script, {console})
  .then(() => {
    console.log("done");
  })
  .catch((e) => {
    console.error(e);
  })

Status and Features

The project is still in early development. Most of the basic language constructs work, and the engine supports an event loop, promises, and generators; but many features are still missing, most notably:

• async/await
• Proxies
• shims for common async API functions;