I am trying to use the async utility for the node.js. Below is my code. The console prints "In my func1" and "In my func2". I also expect it to print "call back func" but it won'nt
var myfunc1 = function(callback) {
var a = 1;
console.log ("In my func1");
};
var myfunc2 = function(callback) {
var b = 2;
console.log ("In my func2");
};
models.Picture.prototype.relativeSort = function(viewer_location) {
console.log("Rel Sort");
var sortedPics = [];
var relsortedPics = [];
// Finds all the pictures
async.series([myfunc1(), myfunc2()],
function(err, results){
if(err) {
throw err;
}
console.log("call back func");
return a+b;
});
};
You need to use the callback argument, for example:
var myfunc1 = function(callback) {
var a = 1;
console.log ("In my func1");
callback(null, 'test');
};
The first argument of callback is an error, and the second the result you want to pass to the final handler.
EDIT
I've missed the other mistake. This line:
async.series([myfunc1(), myfunc2()],
should be
async.series([myfunc1, myfunc2],
You are not supposed to call functions. You are telling async: "Hey, take these functions and do something (asynchronous) with them!".
Related
I am trying to build login system using node.js and i am stuck in this call back function error i have managed to build get login info and check them with data base but when i am verifying password it's taking some time so in there i need to use call back function but even i used callback function it's giving me the same error which is since validation or database call taking time it's executing other stuff in the in my case if conditions.
i have tried to implement this another way just tried to console.log order and all executing opposite this my result first
this is the order that it's run
3
2
undefined
1
but i need run this exactly opposite should i use promises instead of callback?
const {ipcMain} = require('electron');
const Password = require("node-php-password");
const connection = require("./connection");
var hash;
var done;
var self = module.exports = {
getuser_information:function(user_name,pwd,callback){
connection.query("SELECT * FROM `super_admin` WHERE ad_un = ?", user_name, function(err, result, fildes) {
if (err) throw err;
let numbers_retuned = result.length;
hash = result[0].desk;
console.log(1);
});
callback(hash,self.true_or_not);
},
hashverif:function(hash,true_or_not){
true_or_not();
console.log(2);
},
true_or_not:function(){
console.log(3);
return 1
}
}
UPDATE after your comment
You have two errors
Your get_stored_password function returns nothing when your callback function is called that's why console.log(function_returning_nothing()) outputs undefined
You forgot to pass done to your callback function in
get_stored_password's definition callback(done)
const {
ipcMain
} = require('electron');
const Password = require("node-php-password");
const connection = require("./connection");
var hash;
var done;
var self = module.exports = {
get_stored_password: function(name, pwd, callback) {
connection.query("SELECT * FROM `super_admin` WHERE ad_un = ?", name, function(err, result, fildes) {
if (err) throw err;
let numbers_retuned = result.length;
hash = result[0].desk;
if (numbers_retuned == 1) {
var test = pwd;
done = Password.verify(test, hash);
} else {
console.log('no');
return 0;
}
//you must pass an argument to your callback function
// and return done var to get an output when you log this function
callback(done);
return done;
});
},
chek_if_true: function(done) {
console.log(done);
if (done) {
return true;
} else {
return false;
}
}
}
That's why when you log done to the console it's undefined
Here, am calling the method to get the Quickblox result in async method. While i am print the value in console i can get it but the application keep loading not return the result.
Server side:
Meteor.methods({
allquickbloxusers_Methods: function(){
var params = {login: ["99999"]};
var asyncCall = QB1.users.get(params, Meteor.bindEnvironment(function(err, QBuser) {
if(QBuser) {
return QBuser;
} else {
return err;
}
}));
var syncCall = Meteor.wrapAsync(asyncCall);
var res = syncCall();
// now you can return the result to client.
return res;
}
});
To use Meteor.wrapAsync you want to pass it the actual function, not the result of a called function. Like so:
Meteor.methods({
allquickbloxusers_Methods: function(){
var params = {login: ["99999"]};
var syncCall = Meteor.wrapAsync(QB1.users.get)
var res = syncCall(params);
// now you can return the result to client.
return res;
}
});
Basically wrapAsync gives you back a new function that you call with the parameters of the original function.
Knowing this, you can make the function even more concise:
Meteor.methods({
allquickbloxusers_Methods: function(){
var params = {login: ["99999"]};
return Meteor.wrapAsync(QB1.users.get)(params)
}
});
I have a main in nodejs for my program where I need to use my result calculated in a module, but my I don't have the right result.
var myJSONClient = {
"nombre" : "<nombre_cliente>",
"intervalo" : [0,0]
};
var intervalo = gestionar.gestion(myJSONClient,vector_intervalo);
console.log("intervalo: "+intervalo); //return undefined
And this is the module
var gestion = function(myJSON,vector_intervalo) {
var dburl = 'localhost/mongoapp';
var collection = ['clientes'];
var db = require('mongojs').connect(dburl, collection );
var intervalo_final;
function cliente(nombre, intervalo){
this.nombre = nombre;
this.intervalo = intervalo;
}
var cliente1 = new cliente(myJSON.nombre,myJSON.intervalo);
db.clientes.save(cliente1, function(err, saveCliente){
if (err || !saveCliente) console.log("Client "+cliente1.nombre+" not saved Error: "+err);
else {
console.log("Client "+saveCliente.nombre+" saved");
intervalo_final = calculate(vector_intervalo);
console.log(intervalo_final); //here I can see the right content of the variable intervalo_final
}
});
setTimeout(function(){
console.log("pause");
},3000);
console.log(intervalo_final); //result not correct
return intervalo_final;
}
exports.gestion = gestion;
I know that node execute my return without wait the end of my function, for this I can't see the right result, but how can I force my program to wait the end of my function?
I tried with the setTimeout function but wasn't the right way.
You must implement your function just like the other async functions from the API!
First step : give callback to function
var gestion = function(myJSON,vector_intervalo, callback) {
Second step : when the async process is over call callback passing the result (you don't need the return line)
console.log(intervalo_final); //here I can see...
callback(intervalo_final);
Step three: use your function in an async way
gestionar.gestion(myJSONClient,vector_intervalo, function(result){
console.log(result);
});
In async JS you can't return a value the way it seems you trying to do. You need to pass a callback function from your main program when calling gestionar.gestion() (you can add it as a third argument).
Your code sample won't work because function gestion() returns immediately, before intervalo_final content is set.
Something like this:
gestionar.gestion(myJSONClient,vector_intervalo, function callback(intervalo) {
// This is the callback function
console.log("intervalo: " + intervalo);
});
And then within the function:
var gestion = function(myJSON,vector_intervalo, callback) {
...
db.clientes.save(cliente1, function(err, saveCliente) {
if (err || !saveCliente) {
console.log("Client "+cliente1.nombre+" not saved Error: "+err);
if (callback) callback(); // execute callback function without arguments
}
else {
console.log("Client "+saveCliente.nombre+" saved");
intervalo_final = calculate(vector_intervalo);
console.log(intervalo_final);
if (callback) callback(intervalo_final); // your callback function will be executed with intervalo_final as argument
}
});
Also, I highly recommend reading some async javascript tutorial, like http://javascriptissexy.com/understand-javascript-callback-functions-and-use-them/
And Felix's Node.js Guide: http://nodeguide.com/
NEW POST:
Here is the sample of the working async code without a db.
The problem is, if i replace the vars (data1_nodb,...) with the db.collection.find();
function, all needed db vars received at the end and the for() loop ends not
correct. I hope that explains my problem a bit better. OA
var calc = new Array();
function mach1(callback){
error_buy = 0;
// some vars
for(var x_c99 = 0; x_c99 < array_temp_check0.length;x_c99++){
// some vars
calc[x_c99] = new Array();
calc[x_c99][0]= new Array();
calc[x_c99][0][0] = "dummy1";
calc[x_c99][0][1] = "dummy2";
calc[x_c99][0][2] = "dummy3";
calc[x_c99][0][3] = "dummy4";
calc[x_c99][0][4] = "dummy5";
function start_query(callback) {
data1_nodb = "data1";
data2_nodb = "data2";
data3_nodb = "data3";
data4_nodb = "data4";
calc[x_c99][0][0] = data1_nodb;
calc[x_c99][0][1] = data2_nodb;
calc[x_c99][0][2] = data3_nodb;
callback(data1_nodb,data2_nodb,etc..);
}
start_query(function() {
console.log("start_query OK!");
function start_query2(callback) {
data4_nodb = "data5";
data5_nodb = "data6";
data6_nodb = "data7";
calc[x_c99][0][3] = data4_nodb;
calc[x_c99][0][4] = data5_nodb;
callback(data5_nodb,data6_nodb,etc..);
}
start_query2(function() {
console.log("start_query2 OK!");
function start_query3(callback) {
for(...){
// do something
}
callback(vars...);
}
start_query3(function() {
console.log("start_query3 OK!");
});
});
});
}
callback(calc);
};
function mach2(callback){
mach1(function() {
console.log("mach1 OK!");
for(...){
// do something
}
});
callback(calc,error_buy);
};
mach2(function() {
console.log("mach2 OK 2!");
});
OLD POST:
i try to read data from the mongodb and send them back with a callback to the next
function, that needs the infos from the db to proceed.
Without the mongodb read functions it works perfect but now i dont know how
i can send the db vars out of the two inner functions to the first callback function.
Hope someone can help me...
Thanks
var error = 0; var var1 = "yessir";
function start_query(callback) {
var db_name = "db1";
db[db_name].find({name:var1},{data1:1, data2:1, data3:1, data4:1}, function(err, data_catch,callback) {
if( err || !data_catch ) {
console.log("Problem finding data_catch:" + err);
} else {
data_catch.forEach( function(data_catch_finder,callback) {
data1_db = data_catch_finder.data1;
data2_db = data_catch_finder.data2;
data3_db = data_catch_finder.data3;
data4_db = data_catch_finder.data4;
if(data1_db == "" || data2_db == "" || data3_db == "" || data4_db == ""){error = 1; console.log("Error: data_catch_finder");}
callback(data1_db, data2_db, data3_db, data4_db, error);
});
}
});
callback(data1, data2, data3, data4, error);
}
//########################################################################
start_query(function() {
function start_query2(callback) {
console.log("DATA1 from callback:" + data1_db);
console.log("DATA2 from callback:" + data2_db);
console.log("DATA3 from callback:" + data3_db);
console.log("DATA4 from callback:" + data4_db);
var var_no_db = "testing";
//do something else and callback
callback(var_no_db);
}
start_query2(function() {
console.log("Var from callback start_query2:" + var_no_db);
console.log("The end");
});
});
your callback signature are issuing callback as a parameter.
As far as I can understand your code, you need to keep reference of the first callback, the one you receive here: function start_query(callback).
In every callback function you made the mistake to bind the variable name callback to the parameter from the mongo driver (a simple undefined i think).
You can fix it removing every reference of callback from the signature of your inner functions.
a simple example:
function async (cb) {
// params: Error, data
cb(null, 'moo');
}
function foo(callback) {
async(function(err, data, callback){
console.log(callback); // undefined
});
console.log(callback); // Moo
}
foo('Moo');
Take a look at Eloquent Javascript to better understand the JS context switching;
edit
The only way to wait the results of an async function is recall the first callback inside the last nested callback.
function ugly_nested (callback) {
dbquery('...', function(err, data_01) {
if (!! err) return callback(err);
dbquery('...', function(err, data_02) {
if (!! err) return callback(err);
dbquery('...', function(err, data_03) {
if (!! err) return callback(err);
callback(null, data_01, data_02, data_03);
});
});
});
}
ugly_nested(function(err, data01, data02, data03) {
if (!! err) throw err;
manage_data(data01, data02, data03);
});
The FOR loop is synchronous, but, the database calls are asynchronous, so, the for loop will end before the database returns his results. If you really need that for loop you can try out one of the nice flow control libraries out there
ive been trying to use node.js to iterate through an array of cities and make an iterative request to google for directions on each (i then JSON.parse to abstract the drive times). I need to find a way to do this synchronously as otherwise i will just be requesting all the info from google on each city at once. I found a good pattern to use at http://tech.richardrodger.com/2011/04/21/node-js-%E2%80%93-how-to-write-a-for-loop-with-callbacks/ but cannot get the callback to work. As you can see, im using a 'show' function to test the same. My code is as follows:
var request = require('request');
var fs = require('fs');
var arr = ['glasgow','preston','blackpool','chorley','newcastle','bolton','paris','york','doncaster'];
//the function I want to call on each city from [arr]
function getTravelTime(a, b,callback){
request('https://maps.googleapis.com/maps/api/directions/json?origin='+a+'&destination='+b+'®ion=en&sensor=false',function(err,res,data){
var foo = JSON.parse(data);
var duration = foo.routes[0].legs[0].duration.text;
console.log(duration);
});
};
function show(b){
fs.writeFile('testing.txt',b);
};
function uploader(i){
if( i < arr.length ){
show( arr[i],function(){
uploader(i+1);
});
}
}
uploader(0)
The problem I have is that only the first city from the array is output and the callback/iteration never proceeds. Any ideas where im going wrong please?
Thanks for the pointers, was clearly down to my poor understanding of callbacks in javascript. Just reading JavaScript patterns by O'Reilly and hit the 'Callback pattern' sections - doh!
For anyone who doesn't know, this is how the code will work:
var arr = ['glasgow','preston','blackpool','chorley','newcastle','bolton','paris','york','doncaster'];
function show(a,callback){
console.log(a);
callback();
}
function uploader(i){
if( i < arr.length ){
show(arr[i],
function(){
uploader(i+1)
});
};
}
uploader(0)
I was also facing issues like this, so I've written a recursive callback function which will act as a for loop but you can control when to increment. The following is that module, name as syncFor.js and include this in your program
module.exports = function syncFor(index, len, status, func) {
func(index, status, function (res) {
if (res == "next") {
index++;
if (index < len) {
syncFor(index, len, "r", func);
} else {
return func(index, "done", function () {
})
}
}
});
}
//this will be your program if u include this module
var request = require('request');
var fs = require('fs');
var arr = ['glasgow', 'preston', 'blackpool', 'chorley', 'newcastle', 'bolton', 'paris', 'york', 'doncaster'];
var syncFor = require('./syncFor'); //syncFor.js is stored in same directory
//the following is how u implement it
syncFor(0, arr.length, "start", function (i, status, call) {
if (status === "done")
console.log("array iteration is done")
else
getTravelTime(arr[i], "whatever", function () {
call('next') // this acts as increment (i++)
})
})
function getTravelTime(a, b, callback) {
request('https://maps.googleapis.com/maps/api/directions/json?origin=' + a + '&destination=' + b + '®ion=en&sensor=false', function (err, res, data) {
var foo = JSON.parse(data);
var duration = foo.routes[0].legs[0].duration.text;
callback(); // call the callback when u get answer
console.log(duration);
});
};