Detect when all functions of an array return : javascript

Question

I meet a js interview question like this:
There is an array, which items are all functions, these function all need ajax call. Write a function to detect when all functions return result, and return these result. I didn't see original title， so I can't supply more information, I know it need use callback function to count resolve the problem, but I have no idea how to write code because I'm not familiar with js, does anyone can give me some idea with code fragment? Thanks!

Answer 1

Please check following code.. you've to define one counter and one function which will be called whenever ajax call completed in a function it will update the counter and check that all functions completed ajax call or not.. if counter = array length than it means all functions completed their ajax call irrespective of their order. I can't provide you the jsfiddle link because I can't mention url in this code because cross domain ajax url doesn't work so you have to execute this script on your domain.

var counter = 0;

function checkCounter()
{
   if (counter == arr.length)
       alert ("all functions executed from array");
}


var arr = [ 
    function() { $.ajax({ url: ""}).done(function() { counter++; checkCounter() }); }, 
    function() { $.ajax({ url: ""}).done(function() { counter++; checkCounter() }); }
];

for (var i=0; i<arr.length; i++)
{
    arr[i]();
}