Problems with the Javascript proxy pattern

Question

Hi would like to create a function that takes one argument (a function) and proxies the function:

function proxyFunc(func) {
  console.log("Proxying ", func.name);
  var proxied = func;
  func = function() {
   console.log("Calling proxied ", func.name);
   return proxied.apply(this, arguments);
  };
}

Unfortunately the proxying does not work. I already figured out that the assignment of the proxy function to the original function is the problem, but I don't know how to make it work:

func = function() { ... }

You need to return func, otherwise your proxyFunc has no effect. — Eric
– Eric, Commented Nov 20, 2011 at 21:02

Eric · Accepted Answer · 2011-11-20 21:16:25Z

4

Are you looking for this?

function proxyFunc(original) {
    console.log("Proxying ", original.name);
    return function() {
       console.log("Calling proxied " + original.name);
       return original.apply(this, arguments);
    };
}

For what you're doing, this will help:

function proxyMember(obj, member) {
    var original = obj[member];
    console.log("Proxying ", member);
    obj[member] = function() {
       console.log("Calling proxied " + member);
       return original.apply(this, arguments);
    };
}

proxyMember(obj, "foo");

edited Nov 20, 2011 at 21:16

answered Nov 20, 2011 at 21:00

Eric

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4 Comments

Erik Over a year ago

This can be used as Object.func1 = proxyFunc(Object.func1) but I would like to skip the assignment

Eric Over a year ago

@nrabinowitz: Note that you can set name by using var f = function foo(x) { ... }, instead of setting it manually.

Eric Over a year ago

@Erik: You can't. Javascript doesn't pass arguments like that.

nrabinowitz Over a year ago

@Eric - huh, never knew that. But note that MDN marks this as non-standard, and it isn't part of the ECMAScript spec. That page also explains why my approach didn't work, as the property (in implementing interpreters) is read-only.

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