#IUT #Nantes Lectures on NodeJS

getFriendsv1.js

// Mix async (request) + sync (writeFile) style
var request = require('request')
  , async   = require('async')
  , fs      = require('fs')
  , friends = require('./friends');

function getImgPath(friend){
  return './public/'+friend.uid+".jpg";
}

/**
 * Asynchronous Iterator
 * @param  {Object} friend
 * @param  {Function} doneCallback(err, result)
 */
function friendIter(friend, doneCallback){
  request({
    url:friend.pic_big,
    encoding:'binary'
  }, function(err, resp, body){
    if(err){
      doneCallback(err);
      return;
    }
    var file = getImgPath(friend);
    fs.writeFileSync(file, body, 'binary');
    friend.pic_big = file;
    console.log('Downloaded', file);
    doneCallback(null, friend);
  });

}

function everythingsDoneCallback(err, updatedFriends){
  friends = updatedFriends;
  console.log('Done !');
}

async.map(friends, friendIter, everythingsDoneCallback);

getFriendsv2.js

// Full async style

var request = require('request')
  , async   = require('async')
  , fs      = require('fs')
  , friends = require('./friends');

function getImgPath(friend){
  return './public/'+friend.uid+".jpg";
}

/**
 * Asynchronous Iterator
 * @param  {Object} friend
 * @param  {Function} doneCallback(err, result)
 */
function friendIter(friend, doneCallback){
  request({
    url:friend.pic_big,
    encoding:'binary'
  }, function(err, resp, body){
    if(err){doneCallback(err);return;}

    var filepath = getImgPath(friend);

    fs.writeFile(filepath, body, 'binary', function(err){
      if(err){doneCallback(err);return;}

      friend.pic_big = filepath;
      console.log('Downloaded', filepath);
      doneCallback(null, friend);
    });
  });
}

function everythingsDoneCallback(err, updatedFriends){
  friends = updatedFriends;
  console.log('Done !');
}

async.map(friends, friendIter, everythingsDoneCallback);

getFriendsv3.js

// Full async style with concurrent limit

var request = require('request')
  , async   = require('async')
  , fs      = require('fs')
  , friends = require('./friends');

function getImgPath(friend){
  return './public/'+friend.uid+".jpg";
}

/**
 * Asynchronous Iterator
 * @param  {Object} friend
 * @param  {Function} doneCallback(err, result)
 */
function friendIter(friend, doneCallback){
  request({
    url:friend.pic_big,
    encoding:'binary'
  }, function(err, resp, body){
    if(err){doneCallback(err);return;}

    var filepath = getImgPath(friend);

    fs.writeFile(filepath, body, 'binary', function(err){
      if(err){doneCallback(err);return;}

      friend.pic_big = filepath;
      console.log('Downloaded', filepath);
      doneCallback(null, friend);
    });
  });
}

function everythingsDoneCallback(err, updatedFriends){
  friends = updatedFriends;
  console.log('Done !');
}

// https://github.com/caolan/async#maplimitarr-limit-iterator-callback
var concurrent = 5;
async.mapLimit(friends, concurrent, friendIter, everythingsDoneCallback);

getFriendsv4JSHackerVersion.js

// Full async style with concurrent limit
// Read from bottom-up

var request = require('request')
  , async   = require('async')
  , fs      = require('fs')
  , _       = require('lodash') // npm install lodash --save
  , friends = require('./friends');

function getImgPath(friend){
  return './public/'+friend.uid+".jpg";
}

function _onImgFileWritten(fn, friend, err){
  if(err){fn(err);return;}

  friend.pic_big = getImgPath(friend);
  console.log('Downloaded', friend.pic_big);
  fn(null, friend);
}

function _onFriendImgData(fn, friend, err, resp, body){
  if(err){fn(err);return;}

  // MDC .bind() (same as partial function application)
  fs.writeFile(getImgPath(friend), body, 'binary',
    _onImgFileWritten.bind(null, fn, friend));
}

/**
 * Asynchronous Iterator
 * @param  {Object} friend
 * @param  {Function} doneCallback(err, result)
 */
function friendIter(friend, fn){
  request({
    url:friend.pic_big,
    encoding:'binary'
  },
  // MDC .bind() (same as partial function application)
  _onFriendImgData.bind(null, fn, friend));
}

function everythingsDoneCallback(err, updatedFriends){
  friends = updatedFriends;
  console.log('Done !');
}

async.mapLimit(friends, 5, friendIter, everythingsDoneCallback);