How do I trap arguments to a target method when using a Proxy object?

Question

I\'m trying to use Javascript Proxy objects to trap the arguments that are passed to a \'method\' of the target that I\'m proxying.

Please consider this example:

Answer 1

There actually is a way to do this, of course! I just hadn't thought it through thoroughly enough. I can just return a 'proxy' function and trap the arguments in there:

var test = {
    doSomething: function() {
        console.log( arguments.length );
    }
};

var testProxy = new Proxy( test, {
    get: function( target, property, receiver ) {

        switch( property ) {
            case 'doSomething':
              // you just have to return a proxy function
              return function() {
                  // arguments accessible, after all!
                  console.log( 'testProxy::doSomething() arguments.length: ' + arguments.length );

                  // here you can still invoke the original method, of course
                  target[ property ].apply( this, arguments );
              }
            break
        }

        return target[ property ];
    }
} );

testProxy.doSomething( 'this', 'is', 'not', 'so', 'lame', 'after', 'all' );

Answer 2

another snippet : )

const obj_hidden = {};

const obj = new Proxy(obj_hidden, {
    get(target, prop) {
        if (typeof target[prop] == 'function') {
          return function (...args) {
            console.dir({ call: [prop, ...args] });
            return target[prop].apply(target, args);
          }
        }
        console.dir({ get: prop });
        return target[prop];
    },
    set(target, prop, value) {
        console.dir({ set: [prop, value] });
        target[prop] = value;
        return true;
    }
});