Difference between async.each and async.eachSeries

Question

Is async.each working as asynchronous array iterating?

Is async.eachSeries working as synchronous array iterating?(it waits response actually)

I'm asking these because both have callbacks but async.each works like asynchronous array iterating for ex:

//This is traditional way to iterate an array with callback functions in node.js
//Is this same with async.each ? i want to know it actually.

for (var i = 0; i < data.length; i++) {
 (function (i) {
  request(data[i],function(body){
   console.log(body)
  });
 })(i);

//if this codes and async.each are doing same things , 
//i know that async gives me an aert when all finished thats the difference.

Answer 1

Your code example is most similar to what async.each does, as all the async request calls are made at once and allowed to proceed in parallel.

The difference with async.eachSeries is that each iteration will wait for the async operation to complete before starting the next one.

Answer 2

async.eachSeries() applies an asynchronous function to each item in an array in series.

For example, say you have a list of users, each of which needs to post its profile data to remote server log. Order matters in this case because the users in your array are sorted.

async.eachSeries(users, function(user, callback) {
  user.postProfileToServer(callback);
});

async.each() applies an asynchronous function to each item in an array in parallel.

Since this function applies iterator to each item in parallel, there is no guarantee that the iterator functions will complete in order.

async.each(openFiles, saveFile, function(err){

});