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promisesConcurrentWithFailure.js
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promisesConcurrentWithFailure.js
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//imports
var request = require('request'),
mongoClient = require('mongodb').MongoClient,
Q = require('q');
var _db;
Q().then(connectToMongo)
.then(findAllUsers)
.then(fetchAllHomePages)
.then(electBiggest)
.then(console.log)
.catch(function(err){
console.log('in error : ', err);
})
.finally(function(){
_db.close();
})
function connectToMongo(){
var deferred = Q.defer();
mongoClient.connect('mongodb://127.0.0.1:27017/tutoDB', function(err, db) {
if(err) deferred.reject(err);
else {
_db = db;
deferred.resolve(db);
}
});
return deferred.promise;
}
function findAllUsers(){
var deferred = Q.defer();
_db.collection('users').find().toArray(deferred.makeNodeResolver());
return deferred.promise;
}
function fetchAllHomePages(allUsers){
var promises = [];
allUsers.forEach(function(user){
promises.push(fetchHomePage(user));
});
return Q.all(promises).spread(function(){
var homepageWeigths = new Array();
for (var i = 0 ; i < arguments.length; i++){
homepageWeigths.push(arguments[i].length);
}
return homepageWeigths;
});
}
function fetchHomePage(user){
var deferred = Q.defer();
request(user.homepage, function(err, response, body){
if(err || response.statusCode != 200) deferred.reject(err || response.statusCode );
else deferred.resolve(body);
});
return deferred.promise;
}
function electBiggest(weights){
if (weights.length < 1) throw new Error('no page fetched !');
return Math.max.apply(Math, weights);
}