How to call an ajax function in a for loop [duplicate]

Question

I'm new to ajax and JavaScript. What am trying to do is to call an ajax function several times to fetch certain data from a resource and then "push" all of the data into an array so that I can use it later on in the code. Here is my code.

var arr = [];
var users = ["brunofin", "comster404", "ESL_SC2", "OgamingSC2", "cretetion", "freecodecamp", "storbeck", "habathcx", "RobotCaleb", "noobs2ninjas"];

for (i = 0; i < users.length; i++) {
    $.ajax({
        url: "https://api.twitch.tv/kraken/streams/" + users[i],
        success: function(data) {
            arr.push(data);
        },
        error: function(data) {
            arr.push("blank");
        },
        complete: function() {
            if (i == users.length) {
                console.log(arr); //This seem to print even when the condition isn't true
            }
        }
    });
}

The problem with the code is that, it prints to the console even when i isn't equal to users.length

My question is; how do I make certain that it waits until i == users.length is true before it prints to the console? Please keep in mind that I still desire the process to be asynchronous.

Answer 1

Here is how you can call all requests considering their success without running an request over another:

var arr = [];
var users = ["brunofin", "comster404", "ESL_SC2", "OgamingSC2", "cretetion", "freecodecamp", "storbeck", "habathcx", "RobotCaleb", "noobs2ninjas"];

var runRequests = function(userIndex) {
  if (users.length == userIndex) {
    console.log("runRequests Success", arr);
    return;
  }

  var user = users[userIndex];

  $.ajax({
    url: "https://api.twitch.tv/kraken/streams/" + user,
    success: function(data) {
      arr.push(data);
    },
    error: function() {
      arr.push({});
      console.error("runRequests Error", "user", arguments);
    },
    complete: function() {
      runRequests(++userIndex);
    }
  });
};

runRequests(0);

Working demo

Answer 2

This happens because of the asynchronous nature. By the time the ajax callbacks are called, i == user.length is already true. But in your case you can just change:

if (i == users.length) {

to:

if (arr.length == users.length) {

This will also work nice if the callbacks are not executed in the same order as you initiated the ajax requests.