javascript - issue with using .apply on functions

Question

Okay so I have an object and I want to apply a callback function to all of the methods in the object. This is what I have tried so far:

var namespace = { 
  foo : 'bar', 
  foobar :  function() { console.log('call from foobar!')},
  someFunc : function() { console.log('call from someFunc!')},
  someFunc2 : function() { console.log('call from someFunc2!')}
}

var logger = {
  _callback : function () {
    console.log('call from logger!',arguments);
  }
}

for (var m in namespace) { 
  if ( namespace.hasOwnProperty(m) && (typeof namespace[m]=='function') ) {
    logger[m] = namespace[m];
    namespace[m] = function() {
      logger._callback(arguments);
      logger[m].apply(this, arguments);
    }
  }
}

namespace.foobar('foo');
namespace.someFunc('bar');
namespace.someFunc2('bar2');

This is what is getting logged to the console:

call from logger! [["foo"]]
call from someFunc2!
call from logger! [["bar"]]
call from someFunc2!
call from logger! [["bar2"]]
call from someFunc2!

As you can see, for some reason all 3 methods of namespace are outputting 'call from someFunc2! which is wrong. I'm not sure what the issue here is.. what am I doing wrong?

see stackoverflow.com/questions/750486/…

georg
– georg

2014-01-28 01:41:20 +00:00
Commented Jan 28, 2014 at 1:41 — georg
– georg, Commented Jan 28, 2014 at 1:41

Patrick Evans · Accepted Answer · 2014-01-28 01:39:41Z

5

Try

for (var m in namespace) { 
   if ( namespace.hasOwnProperty(m) && (typeof namespace[m]=='function') ) {
      logger[m] = namespace[m];
      (function(index){
         namespace[index] = function() {
           logger._callback(arguments);
           logger[index].apply(this, arguments);
         };
      })(m);
   }
}

otherwise the namespace[m] = function(){} will use whatever m is last

answered Jan 28, 2014 at 1:39

Patrick Evans

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3 Comments

slinkhi Over a year ago

aha, thanks! i'm not sure who to give solve to.. Pointy answered first and explained the problem better, but you showed me an actual code solution D:

Patrick Evans Over a year ago

Go with pointy's since his actually explains what is going on :)

slinkhi Over a year ago

well, he did explain what was going on so i would have eventually arrived at a solution from there, but you saved me the effort of that next step, and he has a lot more rep, so +15 would mean more to you. Also you offered to let him it so I will give it to you.

Pointy · Accepted Answer · 2014-01-28 01:43:02Z

There's just one "m". The code inside that function you create in the for loop references the "live" value of "m", not a value frozen at the point the function was created. The last value it takes on is name "someFunc2", so that's the one that's called.

Step by step:

You create the "namespace" and "logger" objects.
The loop runs. The variable "m" takes on the successive values of the properties in the "namespace" object, and creates a new function for each relevant property of that object.
At the end of the loop, "m" has the value "someFunc2".
You call one of the "namespace" functions. That'll be a call to one of the functions created in the loop. That function will in turn call the "_callback" function. And now the important key point: it references a property of the "logger" object using the value of "m". What is the value of "m"? It's "someFunc2".

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