i need to use the results of this query:
var Back = Parse.Object.extend("Back");
var query = new Parse.Query(Back);
var LastSerialNumber;
query.get("ghxbtU2KSl", {
success: function(result){
LastSerialNumber=result.get("SerialNumber");
return LastSerialNumber;
}
});
alert(LastSerialNumber);
This code doesn't work correctly (it alerts undefined). Why? How can i fix this error?
The query.get() method is asynchronous. That means that your method will exit before the success function gets called. Try this instead:
console.log("start of function");
var query = new Parse.Query('Back')
query.get("ghxbtU2KSl", {
success: function (result) {
console.log("start of callback");
var lsn = result.get("SerialNumber");
alert(lsn);
console.log("end of callback");
}
});
console.log("end of function");
The log statements will help you see the asynchronous call.
Related
I´m having a hard time understanding how to perform this action(as the title says), and maybe someone could help me understand the process, my code is below:
My home-view-model:
var Observable = require("data/observable").Observable;
var ObservableArray = require("data/observable-array").ObservableArray;
var http = require("http");
function createViewModel() {
http.getJSON("http://myJsonfile").then(function (r) {
var arrNoticias = new ObservableArray(r.data);
return arrNoticias;
}, function (e) {
});
}
exports.createViewModel = createViewModel;
I have done a console.log of the arrNoticias before i have putted it inside a callback function and it returns [object object] etc...and then i have done this:
console.log(arrNoticias.getItem(0).titulo);
and it returns the info i need!.
Then in my home.js file i have this:
var observableModule = require("data/observable")
var ObservableArray = require("data/observable-array").ObservableArray;
var arrNoticias = require('./home-view-model.js');
console.log(arrNoticias.getItem(0).titulo);
and the result in the console is:
TypeError: arrNoticias.getItem is not a function. (In 'arrNoticias.getItem(0)', 'arrNoticias.getItem' is undefined)
My question is, how does this action is perform? passing the data from view-model to the .js file?
Thanks for your time
Regards
As that function send a URL request so probably it's an async function, which is on hold while requesting so that's why you get undefined. Normally, you will want your function that sends a URL request to return a promise. Based on that promise, you will the result as expected after the request is done. So:
function createViewModel() {
return new Promise<>((resolve, reject) => {
http.getJSON("http://myJsonfile").then(function (r) {
var arrNoticias = new ObservableArray(r.data);
resolve(arrNoticias);
}, function(e) {
reject(e);
});
}), (e) => {
console.log(e);
})
}
In home.js:
var homeVM= require('./home-view-model.js');
var arrNoticias;
homeVM.createViewModel().then(function(r) {
arrNoticias = r;
});
Is it possible to use $q to fire ajax requests synchronously in AngularJS?
I have a long list of vehicles, each vehicle has events associated with them and I need to retrieve the eventdetails of each event when the user expands the listing.
Right now, if the user expands the listing, I am firing up to 15 calls asynchronously and it seems to be causing issues with the API I'm consuming, so I'd like to see if performance is improved if I wait for each request finishes before firing the next.
I'm attempting to implement $q to delay the next request until the previous is finished, however I can't seem to wrap my head around using the service, here is what I currently have:
// On click on the event detail expander
$scope.grabEventDetails = function(dataReady, index) {
if (dataReady == false) {
retrieveEventDetails($scope.vehicles[index].events);
}
}
var retrieveEventDetails = function(events) {
// events is array
var deferred = $q.defer();
var promise = deferred.promise;
var retrieveData = function(data) {
return $http({
url: '/api/eventdetails',
method: 'POST',
data: {
event_number: data.number
},
isArray: true
});
}
_.each(events, function(single_event) {
promise.then(retrieveData(single_event).success(function(data) {
console.log(data);
}));
});
}
This is still firing asynchronously, Where am I going wrong with this?
I understand firing the requests synchronously isn't the best idea, at the moment I just want to see if performance is improved with the API at all.
You don't need $q to implement a promise as $http returns one.
_.each fires all the callbacks without especially waiting the promise.
All you do is call retrieveData for all events whenever your promise is resolved, and since you don't do a first call, it shouldn't even be working
You could do some recursive call like this :
var retrieveEventDetails = function(events) {
var evt = events.shift();
$http({
url: '/api/eventdetails',
method: 'POST',
data: {
event_number: evt.number
},
isArray: true
}).then(function(response){
console.log(response.data);
retrieveEventDetails(events);
});
}
I do think you should use $q as some other part of your application might need to get a promise.
A good example would be $routeProvider resolve option.
I made a little demo in plunker.
Solution:
retrieveData function should return a function (which returns a promise) instead of a just a promise.
That way we can create a promise chain: promise.then(fn).then(fn).then(fn).then(null,errorFn)
We must resolve the first promise to kick the chain.
var retrieveEventDetails = function(events) {
// events is array
var deferred = $q.defer();
var promise = deferred.promise;
var retrieveData = function(data) {
return function(){
return $http({
url: '/api/eventdetails',
method: 'POST',
data: {
event_number: data.number
},
isArray: true
})
}
}
deferred.resolve();
return events.reduce(function(promise, single_event){
return promise.then(retrieveData(single_event));
}, promise);
}
I'm not sure you even need $q here. In this example, each piece of data is registered in the controller as soon as it comes back from the call.
Live demo (click).
var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope, myService) {
$scope.datas = myService.get();
});
app.factory('myService', function($http) {
var myService = {
get: function() {
var datas = {};
var i=0;
var length = 4;
makeCall(i, length, datas);
return datas;
}
}
function makeCall(i, length, datas) {
if (i < length) {
$http.get('test.text').then(function(resp) {
datas[i] = resp.data+i;
++i;
makeCall(i, length, datas);
});
}
}
return myService;
});
Here's a way using $q.all() that you can wait for all of the data to come through before passing it to the controller: Live demo (click).
var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope, myService) {
myService.get().then(function(datas) {
$scope.datas = datas;
})
});
app.factory('myService', function($q, $http) {
var myService = {
get: function() {
var deferred = $q.defer();
var defs = [];
var promises = [];
var i=0;
var length = 4;
for(var j=0; j<length; ++j) {
defs[j] = $q.defer();
promises[j] = defs[j].promise;
}
makeCall(i, length, defs);
$q.all(promises).then(function(datas) {
deferred.resolve(datas);
});
return deferred.promise;
}
}
function makeCall(i, length, defs) {
if (i < length) {
$http.get('test.text').then(function(resp) {
defs[i].resolve(resp.data+i);
++i;
makeCall(i, length, defs);
})
}
}
return myService;
});
How can I make second AJAX request in the function below asynchronous instead of synchronous? result is a string that should start with 'start of string' and end with 'end of string' but in the middle of the string will be the results of an initial AJAX request that is being iterated.
Foo = {
foo: function() {
$(document).on("change", '.foo', function(e) {
e.preventDefault();
$.ajax({
url: "foo.php",
success: function(rows) {
$.each(rows, function() {
var result = 'start of string'; // START
$.ajax({
url: "bar",
async: false, // I DON'T want this
success: function(data) {
result += data; // MIDDLE
}
});
result += 'end of string'; // END
});
}
});
});
}
}
Thank you.
You can take advantage of jquery deferred objects. You can have two different ajax calls in different functions and then you can use .done() method to make sure you get the final string once both the ajax calls have been completed.
Read more here:
http://api.jquery.com/category/deferred-object/
http://api.jquery.com/deferred.done/
In jquery the way to chain asynchronous calls which are executed one after other, is using promise.then(), which was also called promise.pipe() in previous jquery versions.
Foo = {
foo: function() {
$(document).on("change", '.foo', function(e) {
e.preventDefault();
var param1 = {url: "foo.php"};
var param1 = {url: "bar"};
$.ajax(param1)
.then(function(rows) {
var result = 'start of string'; //START
var fn = function(data) {
result += data;
}
var last, first;
$.each(rows, function() { // rows should be iterable
if (!last) {
first = last = $.ajax(param2).done(fn)
} else {
last = last.then(function(res) {
return $.ajax(param2).done(fn);
});
}
});
last.done(fn).done(function() {
result += 'end of string'; // END
});
return first;
});
});
}
}
The easiest way to do this is indeed by using deferred objects, the example of your JavaScript using the jQuery when and done deferred statements;
$.when(ajaxCallOne()).done(ajaxCallTwo(rows));
function ajaxCallOne() {
return $.ajax({
url : "foo.php",
async: true
});
}
function ajaxCallTwo(rows) {
var result = 'start of string';
$.each(rows, function() {
$.ajax({
url : "bar",
async : true,
success : function(data) {
result += data; // MIDDLE
}
});
result += 'end of string'; // END
});
return result;
}
I'm not a JavaScript nor jQuery expert, but I think you should look at those deferred objects.
http://api.jquery.com/category/deferred-object/
http://api.jquery.com/jQuery.when/
I think you should look at the javascript promise design pattern
let me explain little to you:
This promise is a sort of proxy, representing the future result of the
operation. You would then register a callback on the promise, which
will be executed by the promise once the operation does complete and
the result is available.
Using jQuery you can define promise like this:
var promise = $.getJSON('url');
then using your promise variable you can define what to do when your request is done or failed or even do some function in case it failed or succeded.
promise.done(function(s) {alert('done successfully'); });
promise.fail(function(){ alert('get failed!'); });
promise.always(function(){ alert('this 'll executed anyway!'); });
there are plenty of tutorials on it
Promises and Deferred objects in jQuery
jQuery: Deferred Object
javascript promises
What is the benefit of a 'promise' abstraction in CommonJS?
The variable ajaxdata is modified within the success function, if that hasn't been done yet, I would like to wait 2 seconds, then continue without it.
The use case is for a jqueryui autocomplete field. The autocomplete source is an ajax request, but if the user types quickly, and exits the field before the list loads, the field remains unset. Using the 'change' event on the autocomplete I check if the user entered a valid option without selecting it, but this doesn't work if the source hasn't loaded when the change event fires. So I would like to put a delay in the change function which waits, if the source (stored in the variable 'ajaxdata') is empty.
code:
input.autocomplete({
source: function (request, response){
$.ajax(
{
type: "GET",
url: "/some/url",
dataType: "json",
success: function(data){
response($.map(data,function(item){
return{
label: item.label,
value: item.value
}
}));
ajaxdata = data;
}
}
);
// ajaxopts = ajaxsource(request,response,ajaxurl,xtraqry)
},
change: function(event, ui) {
if (!ui.item) {
// user didn't select an option, but what they typed may still match
var enteredString = $(this).val();
var stringMatch = false;
if (ajaxdata.length==0){
/// THIS IS WHERE I NEED A 2 SECOND DELAY
}
var opts = ajaxdata;
for (var i=0; i < opts.length; i++){
if(opts[i].label.toLowerCase() == enteredString.toLowerCase()){
$(this).val(opts[i].label);// corrects any incorrect case
stringMatch = true;
break;
}
}
}
},
});
Edit:
To be more specific about the problem: This delay needs to be conditional. Meaning that if the data is already loaded (either because it came from a static source, or from an earlier ajax call) I do not want to have a delay.
If I'm understanding you properly, I think you just want to check and see if ajaxdata has been populated; but if it hasn't, only wait two more seconds and then just proceed without it.
Try this:
change: function(event, ui) {
if (!ui.item) {
// user didn't select an option, but what they typed may still match
if (ajaxdata.length==0){
/// THIS IS WHERE I NEED A 2 SECOND DELAY
//pass in 'this' so that you can use it
setTimeout(function() {correctCase(this);}, 2000);
}
}
}
. . . . .
function correctCase(inThis){
//I'm not sure what this variable does. do you really need it???
var stringMatch = false;
var enteredString = $(inThis).val();
//you still want to be sure that ajaxdata is not empty here
if (ajaxdata.length==0){
var opts = ajaxdata;
for (var i=0; i < opts.length; i++){
if(opts[i].label.toLowerCase() == enteredString.toLowerCase()){
$(inThis).val(opts[i].label); // corrects any incorrect case
stringMatch = true; //this variable doesn't seem to do anything after this???
break;
}
}
}
}
I'm not really sure what it is you're trying to do, but I'm pretty sure something like this would be a better way of doing it :
input.autocomplete({
source: function(request, response) {
return $.ajax({
type: "GET",
url: "/some/url",
dataType: "json"
});
},
change: function(event, ui) {
if (!ui.item) {
// user didn't select an option, but what they typed may still match
var enteredString = this.value;
var stringMatch = false;
//make sure ajax is complete
this.source().done(function(data) {
var opts = $.map(data, function(item) {
return {
label: item.label,
value: item.value
}
});
for (var i = 0; i < opts.length; i++) {
if (opts[i].label.toLowerCase() == enteredString.toLowerCase()) {
$(this).val(opts[i].label); // corrects any incorrect case
stringMatch = true;
}
}
});
}
}
});
By default, JavaScript is asynchronous whenever it encounters an async function, it queued that function for later.
But if you want a pause js(ajax call or anything) for you can do it use promises
Case 1: output hello(will not wait for setTimeout)
https://jsfiddle.net/shashankgpt270/h0vr53qy/
//async
function myFunction() {
let result1='hello'
//promise =new Promise((resolve,reject)=>{
setTimeout(function(){
resolve("done");
result1="done1";
}, 3000);
//});
//result = await promise
alert(result1);
}
myFunction();
case 2: output done1(will wait for setTimeout)
https://jsfiddle.net/shashankgpt270/1o79fudt/
async function myFunction() {
let result1='hello'
promise =new Promise((resolve,reject)=>{
setTimeout(function(){
resolve("done");
result1="done1";
}, 3000);
});
result = await promise
alert(result1);
}
myFunction();
How do I do this asynchronously?
var getData, myFunc;
getData = function() {
var data = "";
$.get("http://somewhere.com/data.xml", function(d) {
data = $("#selector", d).html();
});
return data; // does not work, because async callback not yet fired
};
myFunc = function() {
var data = getData();
// do something with data here
};
I am happy to completely re-factor to achieve what I want. I am just don't know what design pattern achieves this.
Well, you can't. You can return a promise though:
var getData, myFunc;
getData = function () {
var d = $.Deferred();
$.get("http://somewhere.com/data.xml", function (data) {
d.resolve($("#selector", data).html())
});
return d.promise();
};
getData().then(function (data) {
alert(data);
});
demo http://jsfiddle.net/W75Kt/2/