How to Emulate Property-Level noSuchMethod in JavaScript?

Emulating Property-Level noSuchMethod in JavaScript

The noSuchMethod feature in certain JavaScript implementations, such as Rhino and SpiderMonkey, allows for handling of unimplemented methods. However, a similar feature is not natively available for properties.

ECMAScript 6 Proxies to the Rescue

ECMAScript 6 introduced Proxies, which provide a mechanism for customizing fundamental operations, including property access. By leveraging Proxy traps, we can emulate the desired behavior for property lookups using __noSuchMethod__.

Solution Using ES6 Proxies

<code class="javascript">function enableNoSuchMethod(obj) {
  return new Proxy(obj, {
    get(target, p) {
      if (p in target) {
        return target[p];
      } else if (typeof target.__noSuchMethod__ == "function") {
        return function(...args) {
          return target.__noSuchMethod__.call(target, p, args);
        };
      }
    }
  });
}</code>

Example Usage

Consider the following example:

<code class="javascript">function Dummy() {
  this.ownProp1 = "value1";
  return enableNoSuchMethod(this);
}

Dummy.prototype.test = function() {
  console.log("Test called");
};

Dummy.prototype.__noSuchMethod__ = function(name, args) {
  console.log(`No such method ${name} called with ${args}`);
  return;
};

var instance = new Dummy();
console.log(instance.ownProp1);
instance.test();
instance.someName(1, 2);
instance.xyz(3, 4);
instance.doesNotExist("a", "b");</code>

This code will log the following output, demonstrating the noSuchMethod emulation for properties:

value1
Test called
No such method someName called with 1,2
No such method xyz called with 3,4
No such method doesNotExist called with a,b

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