How do callbacks work in a recursive call using Javascript?

Question

I want to know how Javascript handles callbacks inside a recursive call, are the callbacks pushed right into the queue on each of the recursive calls or after the call resolves with a base case?

Test case code

function enums(start,end,callback) {
  callback(start);
  if (end == 1)
    return 1;
  else{
    return enums(start + 1, end - 1, callback);
  }
}

var callback = function (number){
   console.log(number);
}
enums(1,10,callback);

You can both test and verify this by simply running your code in the console. As long as you're not running async code, the code is executed in order. — Etheryte
– Etheryte, Commented Aug 10, 2015 at 18:54

Sagi · Accepted Answer · 2015-08-10 19:07:52Z

2

Recursive calls are handled the same way as any other programming language. The code will be as executed as if you were iterating on array and call a function inside the loop. If you would span a timer using setTimeout with a delay of 0 milliseconds after calling your enums function you will notice that the setTimeout callback will be executed after the return of the recursion.

function enums(start,end,callback) {
   callback(start);
   if (end == 1)
      return 1;
   else{
      return enums(start + 1, end - 1, callback);
   }
}

var callback = function (number){
  console.log(number);
}
enums(1,10,callback);
setTimeout(function(){ console.log("Rick"); }, 0);

the output should be: 1..10 and then Rick

answered Aug 10, 2015 at 19:07

Sagi

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