cjsp3

nukedclosure.js

function only(definedItems){
  return new Proxy({}, {
    has(_, prop){
      return !definedItems.includes(prop);
    },
    get(_, prop){
      throw new Error("Referenced variable " + prop.toString() + " out of scope!");
    },
    set(_, prop){
      throw new Error("Referenced variable " + prop.toString() + " out of scope!");
    }
  });
}

const a = 'available';
const b = 'unavailable';

with (only['a', 'console']) {
  console.log(a); // "available"
  console.log(b); // Throws!!
}