Define a Universal/Fallback getter property in JavaScript

Question

JavaScript has getters with Object.defineProperty. So I can define a getter on the property random of window by

Object.defineProperty(window, 'random', {
    get: function () {
        return Math.random();
    }
});

random // Evaluates to a random number

Is it possible to define a "universal getter" for a given object, regardless of the object property? I am looking to do something like

Object.universalGetter(window, function (propertyName) {
     console.log('Accessing property', propertyName, 'of window.');
});

window.Function // Prints "Accessing property Function of window."

Can I do "universal getters" in JavaScript?

possible duplicate of [Is it possible to implement dynamic getters/setters in JavaScript?](http://stackoverflow.com/questions/7891937/is-it-possible-to-implement-dynamic-getters-setters-in-javascript) — user123444555621, Feb 13 '13 at 20:24
Also see http://stackoverflow.com/questions/2266789/is-there-an-equivalent-of-the-nosuchmethod-feature-for-properties-or-a-way — user123444555621, Feb 13 '13 at 20:27

score 17 · Answer 1 · edited Jun 20 '20 at 09:12

Unfortunately: No, there isn't.

There is somehthing called Proxy Objects Introduced in Gecko 18 based Browsers

Which would allow you to do things like this

(function (original, Window) {
  var handler = {
    get: function (target, propertyName) {
      console.log('Accessing property', propertyName, 'of window.');
      return target[propertyName];
    }
  };

  Window = new Proxy(original, handler);


  console.log(Window.setTimeout); 
  // "Accessing property"
  //  "setTimeout"
  //  "of window."
  
  // function setTimeout() {
  //  [native code]
  // }
})(window);

But this is not Standard and still very unstable

Btw I originally thought you could directly use window as local variable in the IIFE but it seems you can't it just logs undefined (wondering why) so I capitalized the "W"

Heres an example on JSBin

Note: You should visit it in Firefox

[`Proxy`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy) is now standard and being implemented as part of ES2015 — CletusW, Aug 31 '16 at 19:11

score 9 · Accepted Answer · 2013-02-13T20:18:03.810

No.

It is not possible to do in ECMAScript 5th edition as there is no provision for this operation. While such is not explicit stated, it can be seen that [GetProperty] does not make any provisions for non-existing properties.

The getters/setters in ECMAScript require existing properties and there is no equivalent of Ruby's method_missing or Python's __getattribute__.

Define a Universal/Fallback getter property in JavaScript

2 Answers2