Node.js | loop over an array , make post calls and accumulate result in an array

Question

Node.js | loop over an array , make post calls and accumulate result in an array

I wish to make a call in Node.js somethine like this (i m using coffeescript for node.js)

test = [] //initially an empty array
list = []//an array with 10 json object

for li in list
  get_data url , li, (err,data) -> test.push data

my get_data method look like

get_data: (url, json_data, callback) ->
  throw "JSON obj is required" unless _.isObject(json_data) 
  post_callback = (error, response) ->
    if error
      callback(error)
    else
      callback(undefined, response)
    return
  request.post {url: url, json: json_data}, post_callback
  return

problem is I am not able to collect the result from request.post into the 'test' array I Know I am doing something wrong in the for loop but not sure what

javascript
node.js
callback
coffeescript

Answer 1

You don't appear to have any way of knowing when all of the requests have returned. You should really consider using a good async library, but here's how you can do it:

test = [] //initially an empty array
list = []//an array with 10 json object

on_complete = ->
  //here, test should be full
  console.log test
  return

remaining = list.length
for li in list
  get_data url , li, (err,data) ->
    remaining--
    test.push data
    if remaining == 0
      on_complete()

Answer 2

In just looking at your code (not trying it out), the problem seems to be a matter of "when you'll get the response" rather than a matter of "if you'll get the response". After your for loop runs, all you have done is queue a bunch of requests. You need to either design it so the request for the second one doesn't occur until the first has responded OR (better) you need a way to accumulate the responses and know when all of the responses have come back (or timed out) and then use a different callback to return control to the main part of your program.

BTW, here is code for a multi-file loader that I created for ActionScript. Since I/O is asynchronous in ActionScript also, it implements the accumulating approach I describe above. It uses events rather than callbacks but it might give you some ideas on how to implement this for CoffeeScript.