Can calls to a module or class be intercepted in node.js/Javascript

Question

In PHP every class contains a "magic" __call function. Using this one can dynamically intercept all calls to a class. For example using

class TestClass {

    public function __call($functionname, $arguments) {

        .. functionname called 

    }

}

See http://www.php.net/manual/en/language.oop5.overloading.php#object.call

Is something similar possible in JavaScript/Node.js? Either on a module (loaded by require) or for classes?

Update: Thank you for all who commented. This does not seem to be possible in pure JavaScript. At least currently.

As bfavaretto pointed out, this can be done using enabling harmony proxies in Node.js. See Enable Harmony Proxies in nodejs.
This question seems to be a duplicate of Get notification when javascript object is invoked.
Possibly related: __noSuchMethod__ (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/noSuchMethod), which is marked nonstandard.

You'll have to wait for the next version of ECMAScript to have that. — bfavaretto, Aug 30 '13 at 21:33
@user2692274 he is referring to `class` and `public` I believe — pllee, Aug 30 '13 at 21:38
@pllee No, I'm referring to [direct proxies](http://wiki.ecmascript.org/doku.php?id=harmony:direct_proxies) — bfavaretto, Aug 30 '13 at 21:42
@bfavaretto that is interesting stuff and looks like nicer syntax but intercepting methods can be done all versions on ECMAScript. — pllee, Aug 30 '13 at 21:48
@pllee: Yes. Ideally I was hoping to replicate the above php code, and intercept the function names of _all_ calls to some class/module. — user2692274, Aug 30 '13 at 21:49
@user2692274 yes that can be done. The answer below can be applied to classes and modules. — pllee, Aug 30 '13 at 21:51
@pllee How can you reproduce `__call` in current js? It's supposed to intercept calls to `someInstance.nonExistingMethod()`. — bfavaretto, Aug 30 '13 at 21:51
@bfavaretto I've never heard of `__call` until now and maybe I am misunderstanding it but you could intercept all methods on an instance. The intercepting method would call `__call` and then the method it just intercepted by doing `return oldMethod.apply(this, arguments)` — pllee, Aug 30 '13 at 21:57
@pllee You're talking about intercepting/overloading existing methods, but `__call` allows you to intercept calls to non-existing methods (see [docs](http://br2.php.net/manual/en/language.oop5.overloading.php#object.call)). You can't do that in js, `var o = {}; o.foo()` throws an error. In PHP, you can intercept such a call with the magic `__call` method. — bfavaretto, Aug 30 '13 at 22:00
@user2692274 I didn't realize you were asking about Node specifically! You can enable that feature in Node, see http://stackoverflow.com/questions/10665892/enable-harmony-proxies-in-nodejs — bfavaretto, Aug 30 '13 at 22:13
@bfavaretto You are right I thought `all calls to a class` meant all method calls. The php docs clear it up. — pllee, Aug 30 '13 at 22:24

score 2 · Answer 1 · edited Sep 30 '15 at 22:24

2

You could do something like this, though it's per-function:

// original module
var module = {
   myFunc: function(){ /* ... */ }
}

// "spying" code

var originalFunction = module.myFunc;

module.myFunc = function(){
    // DO SPY STUFF HERE

    return originalFunction.apply(this, arguments);
};

http://jsfiddle.net/9eu45/

edited Sep 30 '15 at 22:24

Kirby

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answered Aug 30 '13 at 21:38

James Montagne

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Thank you for pointing this out. I was not aware of this functionality. Unfortunately, it is not quite was I am looking for. This might be useful later though! – user2692274 Aug 31 '13 at 08:31

Can calls to a module or class be intercepted in node.js/Javascript

1 Answers1