Implementing Proxy-Based noSuchMethod for Properties

The noSuchMethod feature in JavaScript allows intercepting calls to non-existent methods. However, is there a similar mechanism for properties?

ES6 Proxies to the Rescue

ES6 Proxies provide the ability to customize property access. We can utilize this to emulate a __noSuchMethod__-like behavior for properties:

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);
        };
      }
    }
  });
}

Example Implementation

Here's an example of using the proxy to implement a "Dummy" class that can handle unknown properties:

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}`);
};

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

Usage

• __ownProp1__: Logs the existing property value.
• __test__: Triggers the defined method.
• someName(1, 2)__: Calls a non-existent method with arguments, which is handled by the __noSuchMethod hook.
• __xyz(3, 4)__: Similar to above, but demonstrates that non-function properties can also be handled.
• __doesNotExist("a", "b")__: Logs the absence of a method/property with the provided arguments.