es6 proxies method missing example

method-missing-proxy.js

/*
What happens?
- `new Type().what` is looked up with a call to `get` on the proxy
- a function is returned that will look up `METHOD_NAME` when called
- `METHOD_NAME` is called because of the `()` behind `new Type().what`
- if `METHOD_NAME` exists on you object, your own function is called
- if not, because of prototypal inheritance, `get` is called again
- `name` is now `METHOD_NAME` and we can throw as we know `METHOD_NAME` is not implemented on the type

credits http://soft.vub.ac.be/~tvcutsem/proxies/
*/


var MethodMissingTrap = (function () {

  var METHOD_NAME = "methodMissing";

  return Proxy.create({

    get: function (o, name) {
      if (name === METHOD_NAME) {
        throw new Error("A missing method was called, but your object does not implement '." + METHOD_NAME + "(name, args)'.");
      }
      else {
        return function () {
          var args = [].slice.call(arguments);
          return this[METHOD_NAME](name, args);
        };
      }
    },

    getPropertyDescriptor: function (o, name) {
      return { value: o[name], writable: true, enumerable: true, configurable: true };
    }
  });

})();

// example
function Type () { }
Type.prototype = Object.create(MethodMissingTrap);
Type.prototype.methodMissing = function (name, args) {
  console.log("That wasn't so smart, now, was it?", name, args);
};

new Type().what(1, 2, 3); // That wasn't so smart, now, was it? what [1, 2, 3]