javascript callback guard - prevents a callback to be called twice

cbguard.js

// cbguard by Shimon Doodkin - license: public domain

function cbguard(cb,printerr){ //kind of filter for callbacks. it prevents a callback to be called twice
 var cb1=cb;
 return function() {
  if(cb1) { var cb2=cb1; cb1=false; return cb2.apply(this,arguments); }
  else if(printerr)console.log(new Error('cb called twice').stack);
 }
}

// usage example:
//function myfunction(cb)
//{
//  cb=cbguard(cb);  // usage example
// // or
// // cb=cbguard(cb,true);  // good when developing, it will protect and also tell you you have a problem, here a callback is called twice here.
//
// things that are based on event emitteres are usually have problems with multiple callbacks.

//i used it in a project https://github.com/shimondoodkin/bitcoin-ticker/blob/master/index.js#L46

// in case of callback errors it is possible to trace the error using https://github.com/mattinsler/longjohn
// and writing console.log(new Error('callback trace').stack); in the callback to print from where it was called.

// example:
rates={
 dollar:["USDILS=X",0,"1/1/2000","0:00pm"],
}
var rest = require('restler');
function update_dollar(cb)
{
  cb=cbguard(cb);  // usage example
  try
  { 
  
     rest.get('http://download.finance.yahoo.com/d/quotes.csv?e=.csv&f=sl1d1t1&s=USDILS=X')
     .on('complete', function(data) { 
   
       if(data instanceof Error)
       {
        console.log(data.stack);
        return cb();
       }

       try
       {
        data=JSON.parse("["+data.trim().replace(/""/,"\\\"")+']');
       }
       catch(e)
       {
        console.log(e.stack)
       }
       
       if(typeof data=='object' && data!==null)
         rates.dollar=data;
       cb();
     });
     
  }
  catch(e)
  {
   console.log(e.stack);cb();
  }
  
}

//