How to know which call the current callback is for?

Question

I have a loop making several ajax calls to an API. For each call there would be callback. The problem happen when there's an error and no data is returned, I am not able to know which call made that error.

How do I detect the call that caused this error inside the callback function? here's part of the code:

  for (var i = 0; i < channels.length; i++) {

if ($.inArray(channels[i], livenow) > -1) {

  continue;
}
this.chname = channels[i]; //this is the channel name
Twitch.api({
  method: 'channels/' + this.chname
}, function(error, list) {
//insdie this callback 
//chname may have been changed when we received the callback
  console.log(this.chname + '===>'); 

now, I am not sure what value of chname was called in the API to make the error. when there's no errors, I depend on the data returned from the server to know the callback was a result of which call. when the server return an error, I am not able to know which call this callback is for.

Answer 1

as @boaz suggested, using closure would keep the environment for each call. So, the code would look like :

function mycall(chname) {

function twitchcall() {

Twitch.api({
  method: 'channels/' + chname
}, function(error, list) {
 //callback code would be able to access chname when the twitch call was made
});
};
return twitchcall;}

now to use the closure above, we write the following inside the loop

//now to use it inside the loop
calls[i] = mycall(xchname);
calls[i]();

for a full example http://codepen.io/TamerMarzouk/pen/VabQvP