membranes with dummy target and getPrototypeOf

membrane_dummy_getPrototypeOf.js

load('reflect.js'); // https://github.com/tvcutsem/harmony-reflect/blob/master/reflect.js

function makeMembrane(initTarget) {
  var cache = new WeakMap();
  var revoked = false;
  
  function wrap(target) {
    if (Object(target) !== target) return target; // primitives are passed through
    var wrapper = cache.get(target);
    if (wrapper) return wrapper;
    
    
    var dummyTarget;
    if (typeof target === "function") {
      dummyTarget = target;
    } else {
      dummyTarget = Object.create(wrap(Object.getPrototypeOf(target)));      
    }
      
    wrapper = Proxy(dummyTarget, Proxy(dummyTarget, { // "double lifting"
      get: function(dummyTarget, trapName) {
        if (revoked) throw new TypeError("membrane revoked");
        return function(dummyTarget /*, ...args*/) { // generic trap
          var args = Array.prototype.slice.call(arguments, 1).map(wrap);
          return wrap(Reflect[trapName].apply(undefined, [target].concat(args)));
        }
      }
    }));
    cache.set(target, wrapper);
    return wrapper;
  }
  
  function revoke() { revoked = true; }
  
  return {revoke: revoke, target: wrap(initTarget)};
}

function C(){};
var membrane = makeMembrane(C);
var wrappedC = membrane.target;

// the invariant is preserved across the membrane (both return true)
print(Object.getPrototypeOf(new C()) !== C.prototype.constructor);
print(Object.getPrototypeOf(new wrappedC()) !== wrappedC.prototype.constructor);