I have been trying to get the value of a variable after execution of a for loop in node js. But it is showing as undefined. But the same variable is getting the desired value when I call the variable in setTimeout function after 5000ms. I don't want to use setTimeout because it varies from user to user who uses my application.
The code with which I'm trying is
function getQuestions()
{
for(x=0;x<sevenQIDs.length;x++)
{
var query = connection.query('SELECT QUESTION, OP1, OP2, OP3, OP4, ANS FROM QUESTIONS WHERE QUESTION_ID="'+sevenQIDs[x]+'"', function(err,result,fields){
if(err){
throw err;
}
else{
var a = result[0];
var resTime = [], resAns = [];
resTime.length = 5;
resAns.length = 5;
a.resTime = resTime;
a.resAns = resAns;
sevenQues.push(a);
}
});
}
}
socket.on('socket1', function(text)
{
getQuestions();
console.log(sevenQues);
}
Here sevenQues is a global variable and I'm getting undefined in the console. But when I put this
setTimeout(function()
{
console.log(sevenQues);
},5000);
I'm getting the desired value. Please help me to resolve this issue and I heard of some async.js file which can do the foreach loop to send the desired output. But I'm unable to get this done. Anyhelp would be appreciated.
try this:
function getQuestions(callback)
{
for(x=0;x<sevenQIDs.length;x++)
{
var query = connection.query('SELECT QUESTION, OP1, OP2, OP3, OP4, ANS FROM QUESTIONS WHERE QUESTION_ID="'+sevenQIDs[x]+'"', function(err,result,fields){
if(err){
throw err;
}
else{
var a = result[0];
var resTime = [], resAns = [];
resTime.length = 5;
resAns.length = 5;
a.resTime = resTime;
a.resAns = resAns;
sevenQues.push(a);
if(x == sevenQIDs.length-1) callback();
}
});
}
}
socket.on('socket1', function(text)
{
getQuestions(function(){console.log(sevenQues)});
}
Related
I am getting partial output for the function call. Could anyone tell what I am doing wrong
Data in database in JSON format in MongoDB
DATA IN MONGODB
Function code
async function isTeamNameExists(department, teamID) {
var store = await new Promise(async (resolve, reject) => {
//database read function
db.readCollection(collection_name, (status, data) => {
if (status) {
var teamname = new SB.ListofNames();
teamname.listofboards = data;
var send = teamname;
console.log("send----->", send);
//checking for teamname exists?
for (var boardindex = 0; boardindex < send.listofboards.length; boardindex++) {
var tn = send.listofboards[boardindex];
if (tn.department == department && tn.teamId == teamId) {
resolve(tn);
} else {
resolve(null);
}
}
reject(null);
}
});
});
console.log("store---->", store); // the function return value =store
return (store);
//resolve(store); does not work
}
Function call 1
var output1 = isTeamNameExists(D1,11);
Result-> {department:D1 , teamId:11} // exists ->returns the particular json data of teamId=11
Function call 2
var output2= isTeamNameExists(D2,22);
Result-> null // it should not return null,but it should return {department:D2 , teamId:22}
Function call 3
var output3= isTeamNameExists(D78b,22000211);
Result-> null // it should return null. correct output
> So I am getting partial output. could you tell me what I am doing wrong? I am new to javascript, learning something everyday.
Your function is resolving the moment the first run in the for (var boardindex = 0; boardindex < send.listofboards.length; boardindex++) loop is done because of the else condition.
You want the loop to go through all the items and reject if no entry is found (which you are doing correctly.)
Remove the below part and you'll be good.
} else {
resolve(null);
//resolve(store); does not work will not work because isTeamNameExists function is not a promise.
I am trying to implement a for loop that iterates through a list and subsequently calls two functions, only if the first function results are found.
The issue is that the second function (search.similar) might be taking longer to fetch results.
With the code below, when I run, all of the appropriate output from (search.locate) is correct, but only the last element's results from myList are stored from the (search.similar) function.
ie. all_results = [[cat_res1,mouse_res2],[dog_res1,mouse_res2],[mouse_res1,mouse_res2]]
How do I fix this to append the right results in the right order?
ie. all_results = [[cat_res1,cat_res2],[dog_res1,dog_res2],[mouse_res1,mouse_res2]]
var search = require('./search');
var myList = ['cat','dog','mouse'];
var all_results = [];
for (i=0; i<myList.length; i++){
/* locate function*/
search.locate(myList[i], function (err, searchResult){
if (err){
console.log("Error");
return;
}
if (!searchResult){
console.log("Cannot find it");
return;
}
/*similarity function*/
/* seems to take longer*/
search.similar(myList[i], function (err, similarResult){
if (err){
return;
}
if (!similarResult){
return;
}
var res1 = searchResult.data;
var res2 = similarResult.data;
/* append results to array*/
all_results.push([res1,res2]);
}
});
}
Javascript can be thought of as asynchronous, in that the execution of particular functions do not necessarily happen synchronously, however "describing JavaScript as asynchronous is perhaps misleading. It's more accurate to say that JavaScript is synchronous and single-threaded with various callback mechanisms"
In order to accomplish your goal, though you may still get some ordering issues with the top array, you will need to wrap your .similar() call in another function that takes both arguments. Your reference to the "item" on the top search is changing:
function searchNestedSimilar(item, topRes) {
search.similar(item, function (err, similarResult) {
if (err){
return;
}
if (!topRes){
return;
}
var res1 = topRes.data
var res2 = similarResult.data
// append results to array
all_results.push([res1,res2])
}
}
function searchLocate(item) {
search.locate(item, function (err, searchResult) {
if (err){
console.log("Error");
return;
}
if (!searchResult){
console.log("Cannot find it");
return;
}
searchNestedSimilar(item, searchResults);
}
I encapsulated both calls to keep it modular, but since "item" is in the closure, you really only need the searchLocate() function to wrap your capture your item reference during iteration.
This is a good case for Promises (see Bluebird JS for example http://bluebirdjs.com/docs/getting-started.html) or you could do it with
async.map().
This page talks about it well, too. http://promise-nuggets.github.io/articles/14-map-in-parallel.html
There are many Stack Overflows discussing Promises as well. Understanding JS Promises for example.
A rough example of how to write this with a Promise:
var search = require('./search');
var myList = ['cat','dog','mouse']
var all_results = []
var Promise = require('bluebird');
var locate = Promise.promisify(search.locate);
var similar = Promise.promisify(search.similar);
for (i = 0; i < myList.length; i++){
// locate function
locate(myList[i], function (err, searchResult) {
if (err) {
console.log("Error");
return;
}
if (!searchResult){
console.log("Cannot find it");
return;
}
}).then(function(result) {
//similarity function
similar(myList[i], function (err, similarResult) {
if (err){
return;
}
if (!similarResult){
return;
}
var res1 = searchResult.data
var res2 = similarResult.data
// append results to array
all_results.push([res1,res2])
}).finally(function() {
// NOP
});
});
}
Okay, so my code is pulling data from a yelp business using their official API. My problem is that I can't seem to get the data to return out of the function. The problem isn't in ejs, it's that the data doesn't return when I tell it to! I just get undefined with some attempts, and with others (including the one I'm going to show here), I get an empty array. I'm pasting only the code that's important, let me know if you need more!
function yelp(){
var b = [];
var i = 0;
(struck the initialization of client)
client.business("(struck)", function(error, data) {
if (error != undefined){
res.send("an error occured. exiting");
process.process.reallyExit();
}
b[i++] = data.name;
b[i++] = data.display_phone;
b[i++] = data.rating;
console.log(b); //NEW!!
});
console.log(b);
return b;
}
app.get('/yelp', function(req,res){
var arr = yelp();
console.log(arr);
res.render('yelp.ejs', {title: 'Yelp!', arr: arr});
});
}
I added one more line of code, that I THINK may have narrowed down the problem to being related to my poor internet connection. I added ANOTHER console.log(b), this time inside of the business API call. the console.log(arr) is shows second, the console.log(b); just before the reutrn shows first, and LAST is the console.log(b) INSIDE the API call. It also took a good 30 seconds for that log to appear, and it appeared AFTER the page loaded. So, how do I go about making the page wait for the data? Or is this unrelated to my problem?
Without knowing their API, I do recognize the callback style. The result of the call to your client would then be in the data parameter in the callback, and thats where you want to render your view.
The following is not tested.
function yelp(cb) {
var b = [];
var i = 0;
// (struck the initialization of client)
client.business("(struck)", function(error, data) {
if (error) {
return cb(error);
}
b[i++] = data.name;
b[i++] = data.display_phone;
b[i++] = data.rating;
});
console.log(b);
cb(null, b)
}
app.get('/yelp', function(req, res) {
yelp(function(err, arr) {
if (err) {
res.send("an error occured. exiting");
process.process.reallyExit();
return;
}
console.log(arr);
res.render('yelp.ejs', {
title: 'Yelp!',
arr: arr
});
});
});
The thing to notice here, is the callback passing. This is normally how you do
async work in Node.js. It can be made a bit prettier using promises.
nodejs is async, meaning the app won't wait for the yelp() function to return. you can pass the yelp function a callback like so:
function yelp(callback){
var b = [];
var i = 0;
(struck the initialization of client)
client.business("(struck)", function(error, data) {
if (error != undefined){
res.send("an error occured. exiting");
process.process.reallyExit();
}
b[i++] = data.name;
b[i++] = data.display_phone;
b[i++] = data.rating;
});
console.log(b);
callback(b);
}
yelp(funtion(arr) {
res.render('yelp.ejs', {title: 'Yelp!', arr: arr});
})
You are expecting sync things to happen, but it's async. Your client.business method takes in a callback as it's second argument which isn't returning by the time res.render gets called.
Try this:
function yelp(callback) {
var b = [];
var i = 0;
client.business("(struck)", function(error, data) {
if (error != undefined){
res.send("an error occured. exiting");
process.process.reallyExit();
}
b[i++] = data.name;
b[i++] = data.display_phone;
b[i++] = data.rating;
// No returns in async. Just call the callback.
callback('yelp.ejs', { {title: 'Yelp!', arr: b}})
});
}
app.get('/yelp', function(req,res){
yelp(res.render);
});
I am trying to push some values to array by fetching data from Jenkins APIs, like below.
buildNum = 14;
async.waterfall([
function(callback){
for ( var i = buildNum; i > (buildNum-5); i--) {
(function(){
jenkins.build_info('BuildDefinitionRequest', i, function(err, data) {
if (err){ return console.log(err); }
var tmpObj = {};
tmpObj.jobID = data.fullDisplayName;
tmpObj.result = data.result;
tmpObj.dateTime = data.id;
console.log(tmpObj);
finalArray.push(tmpObj);
});
})();
}
callback(null, finalArray, 1);
},
function(finalArray, value, callback){
console.log(finalArray, value);
callback(null, 'done');
}
],function(err, result){
});
But "callback(null, finalArray, 1);" is getting called before the for loop finish its execution.
When I am printing the value of "finalArray" inside the for loop I am able to see all the values.
Technically the for loop has finished executing, but the jenkins.build_info calls haven't. You cannot make async calls inside of a for loop like that and expect the for loop to only finish after all the calls are complete. You're already using async, so this is an easy fix. I would do something like this:
var buildNum = 14;
var builds = [];
// just builds a collection for async to operate on
for(var i = buildNum; i > (buildNum - 5); i--) {
builds.push(i);
}
var finalArray = [];
async.each(builds, function(build, next) {
jenkins.build_info('BuildDefinitionRequest', build, function(err, data) {
if (err) { next(err); }
var job = {
jobID: data.fullDisplayName,
result: data.result,
dateTime: data.id
};
finalArray.push(job);
next();
});
}, function(err) {
// this won't be called until all the jenkins.build_info functional have completed, or there is an error.
console.log(finalArray);
});
I have a module with a function which generates the value for a vaariable for a variable "stitcheBook". I can see and use this value using a callback.
However, I want to have this value available to me as a module property. How can i achieve this?
Note: I wish the output of the _BookStitcher.stitchAllStories function to go into the _BookStitcher.stitchedBook property.
module.exports = _BookStitcher = (function() {
var db = require('../modules/db');
var stitchedBook = {};
var stitchAllStories = function(callback) {
db.dbConnection.smembers("storyIdSet", function (err, reply) {
if (err) throw err;
else {
var storyList = reply;
console.log(storyList);
// start a separate multi command queue
multi = db.dbConnection.multi();
for (var i=0; i<storyList.length; i++) {
multi.hgetall('story/' + String(storyList[i]) + '/properties');
};
// drains multi queue and runs atomically
multi.exec(function (err, replies) {
stitchedBook = replies;
// console.log(stitchedBook);
callback(stitchedBook);
});
};
});
};
return {
stitchedBook : stitchedBook,
stitchAllStories: stitchAllStories
}
})();
EDIT: to add: I know that I can actually set the value from outside by doing something like this;
_BookStitcher.stitchAllStories(function (reply) {
console.log("Book has been stitched!\n\n")
console.log("the Book is;\n");
console.log(reply);
_BookStitcher.stitchedBook = reply;
console.log("-------------------------------------------------------------------------\n\n\n");
console.log(_BookStitcher.stitchedBook);
});
I was wondering if there was a way of doing it from inside the _BookStitcher module itself.
You could take advantage of how object references work in JavaScript, and assign it to a property:
module.exports = _BookStitcher = (function() {
var db = require('../modules/db');
// CHANGE HERE
var stitched = { book: null };
var stitchAllStories = function(callback) {
db.dbConnection.smembers("storyIdSet", function (err, reply) {
if (err) throw err;
else {
var storyList = reply;
console.log(storyList);
// start a separate multi command queue
multi = db.dbConnection.multi();
for (var i=0; i<storyList.length; i++) {
multi.hgetall('story/' + String(storyList[i]) + '/properties');
};
// drains multi queue and runs atomically
multi.exec(function (err, replies) {
// CHANGE HERE
stitched.book = replies;
// console.log(stitchedBook);
callback(replies);
});
};
});
};
return {
stitched : stitched,
stitchAllStories: stitchAllStories
};
}());
So instead of having it inside _BookStitcher.stitchedBook, you'd have it at _BookStitcher.stitched.book.
But that looks awful, and I'd never use it! You can't know when the value will be available, it's only safe to use it from the callback, when you're sure it's been set.