How to Sync call in Node.js

Question

I have following code snippet:

var  array = [1, 2, 3];
var data = 0;
for(var i=0; i<array.length; i++){
  asyncFunction(data++);
}
console.log(data);
executeOtherFunction(data);

I am expecting value of data as 3 but I see it as 0 due to asyncFunction. How do I call executeOtherFunction when all the asyncFunction calls are done?

Answer 1

If asyncFunction is implemented like the following:

function asyncFunction(n) {
    process.nextTick(function() { /* do some operations */ });
}

Then you'll have no way of knowing when asyncFunction is actually done executing because it's left the callstack. So it'll need to notify when execution is complete.

function asyncFunction(n, callback) {
    process.nextTick(function() {
        /* do some operations */
        callback();
    });
}

This is using the simple callback mechanism. If you want to use one of freakishly many modules to have this handled for you, go ahead. But implementing something like with basic callbacks might not be pretty, but isn't difficult.

var array = [1, 2, 3];
var data = 0;
var cntr = 0;

function countnExecute() {
    if (++cntr === array.length)
        executeOtherFunction(data);
}

for(var i = 0; i < array.length; i++){
    asyncFunction(data++, countnExecute);
}

Answer 2

Use async.each:

var async = require('async');

var data  = 0;
var array = [ 1, 2, 3 ];

async.each(array, function(item, done) {
  asyncFunction(data++, done);
}, function(err) {
  if (err) ... // handle error
  console.log(data);
  executeOtherFunction(data);
});

(assuming that asyncFunction takes two arguments, a number (data) and a callback)

Answer 3

Take a look at this module, I think this is what you're looking for:

https://github.com/caolan/async