Troubles processing data from Async calls - node.js

Question

So this is my task:
You must collect the complete content provided to you by each of the
URLs an d print it to the console (stdout). You don't need to print
out the length, just the data as a String; one line per URL. The catch
is that you must prin t them out in the same order as the URLs are
provided to you as command-line arguments.
And I'm doing it like this:
var http = require('http');
var dataStream = [];
var dataArr = [];
var count = 0;
/*
Function to print results
#dataArr - array
*/
function printResults(dataArr) {
for (var i = 0; i < process.argv.length - 2; i++)
console.log(dataArr[i]);
}
/*
Function to get data from http
#i - int
Getting command line arguments as parametrs.
*/
function httpGet(i) {
http.get(process.argv[2 + i], function(res) {
res.setEncoding('utf8');
res.on('data', function(data) {
dataStream.push(data);
});
res.on('end', function() {
dataArr[i] = (dataStream.join(""));
dataStream = [];
count++;
if (count == process.argv.length - 2) {
printResults(dataArr);
}
});
res.on('error', function(e) {
console.log("Got error: " + e.message);
});
});
}
for (var i = 0; i < process.argv.length - 2; i++) {
httpGet(i);
}
And for some reason sometimes it stores data in array as it supposed, but sometimes it breaks and outputs complete nonsense.
Some results examples:
When working:
$ learnyounode verify program.js
Your submission results compared to the expected:
────────────────────────────────────────────────────────────────────────────
────
1. ACTUAL: "Shazza got us some trackies when as stands out like dog's ba
lls. Grab us a show pony heaps he hasn't got a lurk. She'll be right rubbish
mate it'll be budgie smugglers. You little ripper bloke heaps we're going t
op end. He's got a massive bog standard also built like a freckle. "
1. EXPECTED: "Shazza got us some trackies when as stands out like dog's ba
lls. Grab us a show pony heaps he hasn't got a lurk. She'll be right rubbish
mate it'll be budgie smugglers. You little ripper bloke heaps we're going t
op end. He's got a massive bog standard also built like a freckle. "
2. ACTUAL: "As dry as a sook and as dry as a cleanskin. As cunning as a
metho where get a dog up ya parma. "
2. EXPECTED: "As dry as a sook and as dry as a cleanskin. As cunning as a
metho where get a dog up ya parma. "
3. ACTUAL: "Gutful of gyno how come a mokkies. It'll be clacker and buil
t like a holy dooley!. Get a dog up ya boozer heaps come a captain cook. "
3. EXPECTED: "Gutful of gyno how come a mokkies. It'll be clacker and buil
t like a holy dooley!. Get a dog up ya boozer heaps come a captain cook. "
4. ACTUAL: ""
4. EXPECTED: ""
And an example when it's not working:
$ learnyounode verify program.js
Your submission results compared to the expected:
────────────────────────────────────────────────────────────────────────────
────
1. ACTUAL: "of bogan with it'll be rort. He hasn't got a give it a burl
flamin you little ripper dinky-di. Watch out for the mate's rate to shazza g
ot us some swag. "
1. EXPECTED: "He's got a massive op shop to you little ripper corker. Gutf
ul of bogan with it'll be rort. He hasn't got a give it a burl flamin you li
ttle ripper dinky-di. Watch out for the mate's rate to shazza got us some sw
ag. "
2. ACTUAL: "You little ripper thongs when as stands out like ropeable. T
rent from punchy boardies bloody as cunning as a brisvegas. "
2. EXPECTED: "You little ripper thongs when as stands out like ropeable. T
rent from punchy boardies bloody as cunning as a brisvegas. "
3. ACTUAL: "As dry as a uluru when come a scratchy. Flat out like a ute
with get a dog up ya chrissie. As busy as a fair go no worries it'll be fair
dinkum. She'll be right freo when it'll be cracker. He's Watch got out a fo
r massive the op crook shop my to as you busy little as ripper a corker. bru
mby. Gutful "
3. EXPECTED: "As dry as a uluru when come a scratchy. Flat out like a ute
with get a dog up ya chrissie. As busy as a fair go no worries it'll be fair
dinkum. She'll be right freo when it'll be cracker. Watch out for the crook
my as busy as a brumby. "
4. ACTUAL: ""
4. EXPECTED: ""

Answer 1

Don't treat the data you receive on res.on("data") as an array. Instead, treat it as a string and define it as a variable within the http function (not as a global variable) and do str += data.
Alternatively, you could look at using a library like Async to manage the correct ordering of the async functions you need to execute, as you need each Async to be executed and returned in sequential order.

Answer 2

So the problem was:
Your code makes the assumption that the 3 http responses will not
overlap - that a data event for one response will never occur before
the end event of the previous response, this is not always the case. I
recommend you move the definition of your dataStream variable inside
your httpGet function, this way each request/response will have its
own variable and they cannot interfere with each other, regardless of
timing.
So I refactored my solution to look like this, and now it works 100% of the time:
var http = require('http');
var dataArr = [];
var count = 0;
/*
Function to print results
#dataArr - array
*/
function printResults(dataArr) {
for (var i = 0; i < process.argv.length - 2; i++) {
console.log(dataArr[i].replace('undefined', ''));
}
}
/*
Function to get data from http
#i - int
Getting command line arguments as parametrs.
*/
function httpGet(i) {
http.get(process.argv[2 + i], function(res) {
res.setEncoding('utf8');
res.on('data', function(data) {
dataArr[i] += data;
});
res.on('end', function() {
count++;
if (count == process.argv.length - 2) {
printResults(dataArr);
}
});
res.on('error', function(e) {
console.log("Got error: " + e.message);
});
});
}
for (var i = 0; i < process.argv.length - 2; i++) {
httpGet(i);
}
More info: https://github.com/nodeschool/discussions/issues/1270