async js with node

Question

What is the progression of this function using the async.js library?

var async = require('async');
var square = function (num, doneCallback) {
 console.log(num * num);
 // Nothing went wrong, so callback with a null error.
 return doneCallback(null);
};
// Square each number in the array [1, 2, 3, 4]
async.each([1, 2, 3, 4], square, function (err) {
 // Square has been called on each of the numbers
 // so we're now done!
 console.log("Finished!");
});

In the 'square' function, is the return doneCallback(null) ran every time a new number is passed, or is it ran after all the numbers are finished?

I think it is ran after all the numbers have been passed and console.log'd, IMO the return would interrupt and stop the function. Is this what is actually happening?

• Bergi: Why are you using async at all when square() is synchronous?
• HelloWorld: It's just an example I am using from a blog post I am reading and didn't fully understand how it is working.

Answer 1

No, the doneCallback happens before the return, because the result of the doneCallback is the function's return value. doneCallback will be called once for each time that square is invoked.