Develop Reference

How to create callback function using Ajax?

I am working on the jquery to call a function to get the return value that I want to store for the variable email_number when I refresh on a page.
When I try this:
function get_emailno(emailid, mailfolder) {
$.ajax({
url: 'getemailnumber.php',
type: 'POST',
data : {
emailid: emailid,
mailfolder: mailfolder
},
success: function(data)
{
email_number = data;
}
});
return email_number;
}
I will get the return value as 6 as only when I use alert(email_number) after the email_number = data;, but I am unable to get the value outside of a function.
Here is the full code:
var email_number = '';
// check if page refreshed or reloaded
if (performance.navigation.type == 1) {
var hash = window.location.hash;
var mailfolder = hash.split('/')[0].replace('#', '');
var emailid = 'SUJmaWg4RTFRQkViS1RlUzV3K1NPdz09';
get_emailno(emailid, mailfolder);
}
function get_emailno(emailid, mailfolder) {
$.ajax({
url: 'getemailnumber.php',
type: 'POST',
data : {
emailid: emailid,
mailfolder: mailfolder
},
success: function(data)
{
email_number = data;
}
});
return email_number;
}
However, I have been researching and it stated that I would need to use callback via ajax but I have got no idea how to do this.
I have tried this and I still don't get a return value outside of the get_emailno function.
$.ajax({
url: 'getemailnumber.php',
type: 'POST',
async: true,
data : {
emailid: emailid,
mailfolder: mailfolder
},
success: function(data)
{
email_number = data;
}
});
I am getting frustrated as I am unable to find the solution so I need your help with this. What I am trying to do is I want to call on a get_emailno function to get the return value to store in the email_number variable.
Can you please show me an example how I could use a callback function on ajax to get the return value where I can be able to store the value in the email_number variable?
Thank you.

From the jquery documentation, the $.ajax() method returns a jqXHR object (this reads fully as jquery XMLHttpRequest object).
When you return data from the server in another function like this
function get_emailno(emailid, mailfolder) {
$.ajax({
// ajax settings
});
return email_number;
}
Note that $.ajax ({...}) call is asynchronous. Hence, the code within it doesn't necessarily execute before the last return statement. In other words, the $.ajax () call is deferred to execute at some time in the future, while the return statement executes immediately.
Consequently, jquery specifies that you handle (or respond to) the execution of ajax requests using callbacks and not return statements.
There are two ways you can define callbacks.
1. Define them within the jquery ajax request settings like this:
$.ajax({
// other ajax settings
success: function(data) {},
error: function() {},
complete: function() {},
});
2. Or chain the callbacks to the returned jqXHR object like this:
$.ajax({
// other ajax settings
}).done(function(data) {}).fail(function() {}).always(function() {});
The two methods are equivalent. success: is equivalent to done(), error: is equivalent to fail() and complete: is equivalent to always().
On when it is appropriate to use which function: use success: to handle the case where the returned data is what you expect; use error: if something went wrong during the request and finally use complete: when the request is finished (regardless of whether it was successful or not).
With this knowledge, you can better write your code to catch the data returned from the server at the right time.
var email_number = '';
// check if page refreshed or reloaded
if (performance.navigation.type == 1) {
var hash = window.location.hash;
var mailfolder = hash.split('/')[0].replace('#', '');
var emailid = 'SUJmaWg4RTFRQkViS1RlUzV3K1NPdz09';
get_emailno(emailid, mailfolder);
}
function get_emailno(emailid, mailfolder) {
$.ajax({
url: 'getemailnumber.php',
type: 'POST',
data : {
emailid: emailid,
mailfolder: mailfolder
},
success: function(data)
{
// sufficient to get returned data
email_number = data;
// use email_number here
alert(email_number); // alert it
console.log(email_number); // or log it
$('body').html(email_number); // or append to DOM
}
});
}

Jquery Ajax Call Return

I have made a function which is the one below that i pass data to and returns the result as is. I made this way because i will be needing a lot of ajax call and i just made a function that i pass the data to and get the result as is and work with the result.
function FunctionsCall(data){
var ret;
$.ajax({
type:'GET',
url: 'includes/helpers/functions.php',
dataType:"json",
data: data,
success: function(result){
ret = result;
}});
return ret;}
Now i am calling it where i need it:
$('#register-name, #register-surname').keyup(function(e) {
var x = FunctionsCall({query: $(this).val(), funcid: 1});
(x!==1) ? $(this).addClass('input-has-error') : $(this).removeClass('input-has-error'); });
But strange is that i always see x as undefined. Pointing out the ret is filled with either 1 or 0 i don't know why it is not being passed to x.
Can you please help me out? It might be simple but i just experiment when needed with javascript and jquery.
Regards

ret doesn't get set until the success function runs, which is when the ajax finishes. FunctionCall returns straight away however. You'll either need to return the ajax deferred object or put your addClass/removeClass functionality in your success function.
A way to add your addClass/removeClass functionality to your success function would be like this:
function FunctionsCall(data, successFn) {
$.ajax({
type: 'GET',
url: 'includes/helpers/functions.php',
dataType: "json",
data: data,
success: successFn
});
}
$('#register-name, #register-surname').keyup(function(e) {
var element = $(this);
var data = { query: element.val(), funcid: 1 };
var successFn = function(x) {
if (x !== 1) {
element.addClass('input-has-error')
} else {
element.removeClass('input-has-error');
}
}
FunctionsCall(data, successFn);
});

The problem is that the ajax call takes time to execute, whereas your processing of x is immediately after the call to FunctionsCall
Imagine that in order to go to the php file and get the result, the browser has to send a request over the wire, the server needs to process the request and return the value, again over the wire. This process takes an unpredictable amount of time as it relies on network connections and server specs / current load.
The code to call the function and process the result happens immediately after this step and as such won't have the required values when it is run (browsers are much quicker at executing the next step than networks are at processing requests).
The best thing to do is to wrap your processing code up in it's own function, so it isn't immediately called, then call that function with the result once you get it. Like this:
// function defined, won't be called until you say so
var processMe = function(result) {
alert(result);
}
$.ajax({
// ajax params
success: function(result) {
// function called within success - when we know the request is fully
// processed, however long it takes
processMe(result));
}
});
You could also do the processing directly in the success block but the advantage of using a function is it's there to re-use in the future, plus, you also get to give it a nice understandable name, like outputValidatedMessage.

you must send ajax request syncronous
function FunctionsCall(data){
var ret;
$.ajax({
type:'GET',
async: false,
url: 'includes/helpers/functions.php',
dataType:"json",
data: data,
success: function(result){
ret = result;
}
});
return ret;
}

Ajax calls are asynchronous.
This means that while you call $.ajax(), the function continues to run and return x which is undefined, as the ajax response has not been send yet.
function FunctionsCall(data){
var ret;
$.ajax({
type:'GET',
async: false,
url: 'includes/helpers/functions.php',
dataType:"json",
data: data,
success: function(result){
ret = result;
}
});
return ret;
}

The below should work for you
function FunctionsCall(data){
var ret;
$.ajax({
type:'GET',
url: 'includes/helpers/functions.php',
dataType:"json",
data: data,
success: function(result){
(result !==1 ) ? $(this).addClass('input-has-error') : $(this).removeClass('input-has-error'); });
}});
}

maybe is because the ajax function is called asynchronously so the line var x= .... doesn't wait for the asignment and thats why is undefined. for that you should use a promise here is an example http://joseoncode.com/2011/09/26/a-walkthrough-jquery-deferred-and-promise/
http://www.htmlgoodies.com/beyond/javascript/making-promises-with-jquery-deferred.html

check if the following works, may be your GET method is taking time to execute.
var x;
function FunctionsCall(data){
var ret;
$.ajax({
type:'GET',
url: 'includes/helpers/functions.php',
dataType:"json",
data: data,
success: function(result){
ret = result;
x= result;
alert(x)
}});
return ret;}
if the snippet works, you should make you synchronous async: false or make callback function

try this code.
function FunctionsCall(data,callback) {
try {
ajax({
type: 'GET',
url: 'includes/helpers/functions.php',
dataType: "json",
data: data,
success: function (result) {
callback(result);
}
});
} catch(e) {
alert(e.description);
}
}
$('#register-name, #register-surname').keyup(function (e) {
var data = {
uery: $(this).val(),
funcid: 1
};
FunctionsCall(JSON.stringify(data), function (result) {
(result !== 1) ? $(this).addClass('input-has-error') : $(this).removeClass('input-has-error');
});
});

Set variables in JavaScript once function finishes

I have two functions that makes Ajax calls: getData and getMoreData. getMoreData requires a url variable that is dependent on the url variable getData. This questions continues from: String append from <select> to form new variable.
By appending an item obtained from the received from getData onto a base URL, I create a new variable (Let's call this NewDimensionURL) that I use for getMoreData url. However, NewDimensionURL will show error because the original list (from getData) has yet to be populated and will append nothing onto the base URL.
An idea that I have is to set NewDimensionalURL once getData finishes populating the combobox, so that getMoreData can run after.
JavaScript
var GetDimensions = 'SomeURL1';
//--Combines URL of GetDimensionValues with #dimensionName (the select ID)
var UrlBase = "Required URL of getMoreData";
var getElement = document.getElementById("dimensionName");
var GetDimensionValues = UrlBase + getElement.options[getElement.selectedIndex].text;
function handleResults(responseObj) {
$("#dimensionName").html(responseObj.DimensionListItem.map(function(item) {
return $('<option>').text(item.dimensionDisplayName)[0];
}));
}
function handleMoreResults (responseObj) {
$("#dimensionId").html(responseObj.DimensionValueListItem.map(function(item) {
return $('<option>').text(item.dimensionValueDisplayName)[0];
}));
}
function getData() {
debugger;
jQuery.ajax({
url: GetDimensions,
type: "GET",
dataType: "json",
async: false,
success: function (data) {
object = data;
handleResults(data);
}
});
}
function getMoreData() {
debugger;
jQuery.ajax({
url: GetDimensionValues,
type: "GET",
dataType: "json",
async: false,
success: function (data) {
object = data;
handleMoreResults (data);
}
});
}
Answered
Reordered as:
var GetDimensionValues;
function handleResults(responseObj) {
$("#dimensionName").html(responseObj.DimensionListItem.map(function(item) {
return $('<option>').text(item.dimensionDisplayName)[0];
}));
GetDimensionValues = UrlBase + getElement.options[getElement.selectedIndex].text;
}
Created onchange function Repopulate() for getMoreData() to parse and for handleMoreResults() to populate.

I'm guessing you just do getData(); getMoreData() back to back? If so, then you're running getmoreData BEFORE getData has ever gotten a response back from the server.
You'll have to chain the functions, so that getMoreData only gets executed when getData gets a response. e.g.
$.ajax($url, {
success: function(data) {
getMoreData(); // call this when the original ajax call gets a response.
}
});

Without seeing your code it's hard to say if this is the right solution, but you should try chaining the functions:
$.ajax({url: yourUrl}).then(function (data) {
// deal with the response, do another ajax call here
}).then(function () {
// or do something here
});

how to use properties and methods withing a JavaScript class to exchange data?

i have small issue with exchanging data in between methods in a JavaScript object (class):
var TEST = (function () {
var TEST = function() {
};
TEST.prototype.get = function() {
$.ajax({
type: "GET",
url: "http://test.com/getall",
dataType: "json",
success: function (data) {
return data; // if i console log this i will get a json obj
}
});
};
TEST.prototype.parse = function(data) {
$.each(this.get(), function(k, v){
console.log(v);
});
};
return TEST;
})();
so i am trying to call one method in the each statement in another method. the issue is that
the response is undefined.
i also tried it like this, but with he same result
var testing = new TEST();
var get = testing.get();
testing.parse(get);
What am i missing? how can i return the data from this.get to be used in this.parse.
thanks

$.ajax() per default is asynchronous. That means, that the execution of your function get() wont wait until the request is finished. Hence you return no value from it, which results in undefined being returned.
In order to have your get() function be able to return a value, you would have to do the request in a synchronous way and set a variable in the outer function (as success itself is just another function, whose return value is not caught):
TEST.prototype.get = function() {
var result;
$.ajax({
type: "GET",
url: "http://test.com/getall",
async: false, // this is the important part!
dataType: "json",
success: function (data) {
result = data;
}
});
return result;
};
EDIT
As mentioned by #pebbl, this will halt the execution of all your scripts, until the request is done. Hence your whole page will be blocked for the time being.
The general approach is to use callbacks in such cases, which will be executed once the requests finished. So in your case something like this:
TEST.prototype.get = function( cb ) {
$.ajax({
type: "GET",
url: "http://test.com/getall",
dataType: "json",
success: function (data) {
cb( data );
}
});
};
with later on calling like this:
var testing = new TEST();
testing.get( function( data ) {
testing.parse( data );
});

You can't construct your function this way as you are relying on an asyncronous call, which will return it's result outside of the normal execution flow. The only way you can actually receive the result of your .get function is to use a callback.
Put simply your value isn't being returned from the .get function, it's being returned from the callback you are passing into jQuery's .ajax method.
You'd be far better off redesigning your code so as to still support the asyncronous call -- rather than disabling async.
A rough idea is to change your parse function like so:
TEST.prototype.parse = function(data) {
this.get(function(result){
$.each(result, function(k, v){
console.log(v);
});
});
};
And to change your get function accordingly:
TEST.prototype.get = function(callback) {
$.ajax({
type: "GET",
url: "http://test.com/getall",
dataType: "json",
success: callback
});
};
The above is just a quick example, you'd be wise reading up on the following jQuery topics:
http://api.jquery.com/promise/
http://api.jquery.com/category/deferred-object/
If you design your code around the promise pattern you'll find it complicated at first, but it gives you a lot of power in your code -- and gets around the whole callback stacking madness you can end up with when dealing in ajax calls.
Whilst it's not entirely clear from the jQuery.ajax documentation, this function returns a jqXHR object which implements the promise interface. So this means you can use the promise methods done, always and fail.
http://api.jquery.com/jQuery.ajax/

Declaring global variable

I know that this question has been asked million times so my apologies.
I looked at all other examples and I dont understand why the following code is not working now.
I get undefined alert box when I place it outside the CheckinMap function.
Why is it?
$(document).ready(function() {
var MapData;
$(function CheckinMap() {
$.ajax({
type: "GET",
url: "content/home/index.cs.asp?Process=ViewCheckinMap",
success: function (data) {
MapData = data;
},
error: function (data) {
$("#checkinmap").append(data);
}
});
});
alert(MapData);
});

MapData is undefined because the alert is executed while the ajax call is still running (ajax is asynchronous) and the response is not yet available. So change your code in this way
success: function (data) {
MapData = data;
alert(MapData);
},
or continue the code execution calling another function
success: function (data) {
continueExecution(data)
},
...
function continueExecution(data) {
alert(data)
}
or use deferred objects (on jQuery 1.5+)
$.ajax({
type: "GET",
url: "content/home/index.cs.asp?Process=ViewCheckinMap"
})
.done(function(data) { alert(data) })

The execution order is asynchronous. Currently the following steps are executed:
Ajax call
alert(MapData); // unknown
success function that sets MapData (or the error function that doesn't even set MapData)
You could alert in the success function (like suggested), but then you don't know if the variable is local to that function or is actually global. To test if MapData is actually global you can use setTimeout to alert the variable back.
Check out this modified example code:
// Global variable
var MapData;
// Global function
function test() {
alert(MapData);
}
$(document).ready(function() {
$.ajax({
type: "GET",
url: "http://www.google.nl",
success: function (data) {
MapData = data;
// Call global function with timeout
setTimeout(test, 10);
},
error: function (data) {
$("#checkinmap").append(data);
// Set error message instead of data (for testing)
MapData = 'error';
// Call global function with timeout
setTimeout(test, 10);
}
});
});
Or you can test it out here: http://jsfiddle.net/x9rXU/