callback in nested function

Question

i have a function which calls the another function and so on.

function A(args,callback){ 
// make ajax request
// on response 
 B() 
}
function B(args){
// make ajax request
// on response 
 C()
}
function C(args){
 // make ajax request
 // on response 
 D()
}

I am making such ten ajax calls. Two questions...

1. can anyone explain me what is callback-hell? Is this a callback Hell?
2. If i call callback() inside function D, will it get called. I am not passing callback as argument to my other functions.

• Evan Trimboli: I would think really hard before doing 10 ajax calls in a row that all depended on each other, if that's what you're saying.
• apsillers: I'm not familiar with a well-established definition for "callback hell", but I would call many deeply-nested callbacks "callback spaghetti".
• gdoron: @apsillers. LOL, my thoughts exactly, BTW I've found the definition to that phrase, look below.
• theJava: @EvanTrimboli: Is there any better way to do it?

Answer 1

1. I don't know what you're calling callback hell but it's one hell of a spaghetti code.

What is "callback hell"?
Asynchronous javascript, or javascript that uses callbacks, is hard to get right intuitively.

Source

2.No, callback is not defined inside D so you will get an Error.

• theJava: Lets take if i pass my callback reference from A to B and C then receive it in D... will i able to achieve.
• gdoron: @theJava, Yes, in that case it will be valid, probably spaghetti but valid. I've never seen a good reason for doing 10 async operations one after the other. usually when those kind of things are being done, it's a mistake.

Answer 2

Inside D() there is no way to call callback because it is not defined there. What I mean by this is as long as you don't pass arguments down the callbacks then you are not having your callback variable inside D(). Callback hell is a situation where callbacks call each-other meaning A() calls B() and B() calls A().

• Bergi: Imho you don't need (endless) "recursion" for a callback hell.
• Konstantin Dinev: @Bergi You are right, but callbacks are not that hard to debug, but the real hell is when callbacks are constantly calling each-other, because then debugging results in a different output than what you would get if you do not breakpoint inside the callbacks :)
• theJava: If i pass my callback reference via A to B and B to C an then C to D... will that result in callback hell
• Konstantin Dinev: @theJava This begs to the question is dynamic programming a callback hell? In your case I would not call it a callback hell.

Answer 3

We can pass function reference as a parameter in JavaScript and use this reference to call related function whenever/ wherever we want.

for more info see this link http://recurial.com/programming/understanding-callback-functions-in-javascript/