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Javascript - why is this undefined?

The alert at the start shows "undefined", why?
The alerts come in this order:
"success!"
"Data" (what it should be)
"undefined"
I read through multiple threads, the problem was always that ajax was asynchronous, so the data was not defined when it was accessed, but in my case the data is there, the alert in my function shows the data BEFORE the other alert where it is undefined!
Very grateful for any help!
I got this code
var data = getData("");
alert(data); <<<<<<< UNDEFINED
function getData(fileName) {
$.ajax({
async:false,
type: "GET",
url: "breastCancer.csv",
dataType: "text",
success: function (data) {
var arrData = processData(data);
alert("success!");
alert(arrData); <<<<< WORKS GREAT
return arrData;
},
});
}
function processData(data) {
var arrData = CSVToArray(data);
dimensions = arrData[0];
var objects = [];
objects[0] = dimensions;
for (var i = 1; i < arrData.length; i++){
objects[i] = new Object();
for (var j = 0; j < dimensions.length; j++){
objects[i][dimensions[j]] = arrData[i][j];
}
}
return objects;
}
To clarify, I know asynchronous is the way to go for user experience, but this page just has to show data from this call, so its okay for me to wait for it.

Your getData function doesn't return anything.

You need to return it from the function itself.
function getData(fileName) {
$.ajax({
async:false,
type: "GET",
url: "breastCancer.csv",
dataType: "text",
success: function (data) {
var arrData = processData(data);
alert("success!");
alert(arrData); <<<<< WORKS GREAT
return arrData;
},
});
}
^ This returns the data within getData. But getData doesn't do anything with it: such as returning it.
function getData(fileName) {
var ourData = "";
$.ajax({
async:false,
type: "GET",
url: "breastCancer.csv",
dataType: "text",
success: function (data) {
var arrData = processData(data);
ourData = arrData;
},
});
return ourData;
}
This returns the data from getData to whatever calls that function.
edit: also, don't use async:false. Your browser won't capture any events happening until that AJAX completes. The benefit of asynchronous JS is that...we can! And in this case should.

Preface: Don't use async: false. But answering the question:
getData doesn't return anything. You're doing a return from the success callback, but that returns something from the success callback, not getData.
To change it so getData returns something, you'd do this:
function getData(fileName) {
var arrData;
$.ajax({
async:false,
type: "GET",
url: "breastCancer.csv",
dataType: "text",
success: function (data) {
arrData = processData(data);
},
});
return arrData; // <=== Now `getData` returns something
}
But don't do that. Instead, embrace asynchronous programming and remove async: false. For instance, a callback:
function getData(fileName) {
$.ajax({
async:false,
type: "GET",
url: "breastCancer.csv",
dataType: "text",
success: function (data) {
callback(processData(data));
},
});
}
...called like this:
getData(function(data) {
alert(data);
});
...or a promise ($.ajax returns one, of sorts):
function getData(fileName) {
return $.ajax({
async:false,
type: "GET",
url: "breastCancer.csv",
dataType: "text",
success: function (data) {
callback(processData(data));
},
}).then(data) {
return processData(data); // <== Becomes the resolution value of `getData`'s promise
});
}
and then
getData().then(function(data) {
alert(data);
});

data is undefined because the function getData doesn't return anything. You should have a look at promises.

multiple ajax call to single function javascript

I have 3 ajax call. Data from each ajax call is passed to john_doe();
Call 1
$.ajax({
url: url1,
dataType: "JSON",
type: "GET",
}).success(function(data1){
john_doe(data1);
});
Call 2
$.ajax({
url: url2,
dataType: "JSON",
type: "GET",
}).success(function(data2){
john_doe(data2);
});
Call 3
$.ajax({
url: url3,
dataType: "JSON",
type: "GET",
}).success(function(data3){
john_doe(data3);
});
Main function
function john_doe(param){
console.log(param); //Print data from all three ajax call.
}
How to separate data1, data2 and data3 in john_doe function? because I need to carry out arithmetic operation.
Currently,
Input
data1 = one,two,three
data2 = four
data3 = five
Output
console.log(param) would give output as
one
four
five
I want output as
console.log(param[0])
console.log(param[1])
console.log(param[2])
param[0] containing one,two,three
param[1] containing four
param[2] containing five
I dont have control over the data. How to access data1, data2 and data3 separately?

Using promises you can access all the data in Promise.all() callback and do whatever you need with it all at once. Assumes using jQuery 3+. Can use $.when in older versions
var urls =['data-1.json','data-2.json','data-3.json'];
// array of ajax promises
var reqPromises = urls.map(function(url){
return $.ajax({
url: url,
dataType: "JSON",
type: "GET"
});
});
Promise.all(reqPromises).then(function(res){
// res is array of all the objects sent to each `$.ajax` from server
// in same order that urls are in
var param = res.map(function(item){
return item.val
});
console.log(param)
})
DEMO

Quick and dirty solution is simply pass in an identifier, why is this dirty because it isn't really extensible with respect to adding say 4th or 5th call each time you do this you need to add more identifiers and your if statement in the main method will end up pretty ugly at one point. But that said sometimes "Keeping It Simple" is ok.
Main function:
function john_doe(identifier, param) {
// best to use something more readable then numbers
if(identifier == 1) {
console.log(param); //Print data from all ajax call 1.
} else if(identifier == 2) {
console.log(param); //Print data from all ajax call 2.
} else if(identifier == 23) {
console.log(param); //Print data from all ajax call 3.
} else {
// handle bad id
}
}
In your ajax calls, pass in the right identifier, for example Call 2:
$.ajax({
url: url2,
dataType: "JSON",
type: "GET",
}).success(function(data2){
// numeric 2 in in the first param is your identifier
john_doe(2,data2); });

Adding a param to let you know where it is being called from
Call 1
$.ajax({
url: url1,
dataType: "JSON",
type: "GET",
}).success(function(data){
john_doe('call1',data);
});
Call 2
$.ajax({
url: url2,
dataType: "JSON",
type: "GET",
}).success(function(data){
john_doe('call2',data);
});
Call 3
$.ajax({
url: url3,
dataType: "JSON",
type: "GET",
}).success(function(data){
john_doe('call3',data);
});
Main function
function john_doe(call,data){
console.log('Called from : ' + call);
console.log(data); //Print data from all three ajax call.
}

How about this?
Declare an object container to hold your response data values and your arithmetic operation function.
var myParams = {
all_params: [],
getParams: function(){
return this.all_params;
},
setParam: function(index, data){
this.all_params[index] = data;
},
yourArithmeticOperation: function(){
console.log(this.all_params); // your actual logic using all 3 ajax response data
}
}
Then, in your ajax calls:
// call 1
$.ajax({
url: url1,
dataType: "JSON",
type: "GET",
}).success(function(data){
myParams.setParam(0, data); // add ajax 1 response data
});
// call 2
$.ajax({
url: url1,
dataType: "JSON",
type: "GET",
}).success(function(data){
myParams.setParam(1, data); // add ajax 2 response data
});
// call 3
$.ajax({
url: url1,
dataType: "JSON",
type: "GET",
}).success(function(data){
myParams.setParam(2, data); // add ajax 3 response data
});
In case you need all your response data,
// after all three ajax calls
params = myParams.getParams();
console.log(params);
And finally, your arithmetic operation,
myParams.yourArithmeticOperation();

try adding async: false to your ajax calls
$.ajax({
url: url1,
dataType: "JSON",
type: "GET",
async: false,
}).success(function(data){
john_doe('call1',data);
});

Jquery set HTML via ajax

I have the following span:
<span class='username'> </span>
to populate this i have to get a value from PHP therefor i use Ajax:
$('.username').html(getUsername());
function getUsername(){
$.ajax({
type: 'POST',
url: myBaseUrl + 'Profiles/ajax_getUsername',
dataType: 'json',
data: {
},
success: function(data){
document.write(data);
}
})
}
Now when i debug i see that the returned data (data) is the correct value but the html between the span tags stay the same.
What am i doing wrong?
Little update
I have tried the following:
function getUsername(){
$.ajax({
type: 'POST',
url: myBaseUrl + 'Profiles/ajax_getUsername',
dataType: 'json',
data: {
},
success: function(data){
$('.username').html('RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRr');
}
})
}
getUsername();
Still there is no html between the tags (no text) but when i look at the console the method is completed and has been executed.
Answer to the little update
The error was in my Ajax function i forgot to print the actual response! Thank you for all of your answers, for those of you who are searching for this question here is my Ajax function:
public function ajax_getUsername(){
if ($this->RequestHandler->isAjax())
{
$this->autoLayout = false;
$this->autoRender = false;
$this->layout = 'ajax';
}
print json_encode($this->currentClient['username']);
}
Do note that i am using CakePHP which is why there are some buildin methods. All in all just remember print json_encode($this->currentClient['username']);

The logic flow of your code is not quite correct. An asynchronous function cannot return anything as execution will have moved to the next statement by the time the response is received. Instead, all processing required on the response must be done in the success handler. Try this:
function getUsername() {
$.ajax({
type: 'POST',
url: myBaseUrl + 'Profiles/ajax_getUsername',
dataType: 'json',
data: { },
success: function(data){
$('.username').html(data); // update the HTML here
}
})
}
getUsername();

Replace with this
success: function(data){
$('.username').text(data);
}

In success method you should use something like this:
$(".username").text(data);

You should set the html in callback
function getUsername() {
$.ajax({
type: 'POST',
url: myBaseUrl + 'Profiles/ajax_getUsername',
dataType: 'json',
data: {
},
success: function(data){
$('.username').html(data);
}
})
}

Add a return statement for the function getUsername
var result = "";
$('.username').html(getUsername());
function getUsername(){
$.ajax({
type: 'POST',
url: myBaseUrl + 'Profiles/ajax_getUsername',
dataType: 'json',
data: {
},
success: function(data){
document.write(data);
result = data;
}
})
return result;
}

You can use .load()
Api docs: http://api.jquery.com/load/
In your case:
$('.username').load(myBaseUrl + 'Profiles/ajax_getUsername',
{param1: value1, param2: value2});

Why can't I do .ajax ( return data; )? jQuery

I'm trying to get my function to return the data it got into another function but it doesn't seem to work? How can I get it to return the data?
function playerid(playername) {
$.ajax({
type: "POST",
url: "fn.php?playerid",
data: "playername="+playername,
success: function(data) {
//$("#test").text(data);
return data;
}
});
}
I want to use it in another function like this
showBids(playerid(ui.item.value));
function showBids(playerid) {
$.ajax({
type: "POST",
url: "poll.php?",
async: true,
dataType: 'json',
timeout: 50000,
data: "playerid="+playerid,
success: function(data) {
//.each(data, function(k ,v) {
//})
//$("#current_high").append(data);
setTimeout("getData()", 1000);
}
});

First of all, your playerid() does not return anything, so what do you want to use? It has only $.ajax() call in it, no return statement (one of the callbacks in $.ajax() has return statement, but see below).
Secondly, JavaScript does some things asynchonously, otherwise every interface element would need to wait to react to user action until the AJAX call returns from the server.
Use event-based approach, by passing callbacks to some functions. Then, after they finish, just call the callbacks passing them the result:
function getplayerid(playername, callback) {
$.ajax({
type: "POST",
url: "fn.php?playerid",
data: "playername="+playername,
success: function(data) {
//$("#test").text(data);
callback(data);
}
});
}
and then use it like that:
getplayerid(ui.item.value, showBids);
(notice function name change since it does not actually return player ID, it gets it and passes it to callback)

You could try to use syncronous Ajax:
function playerid(playername) {
return $.ajax({
type: "POST",
url: "fn.php?playerid",
data: "playername="+playername,
async : false //making Ajax syncronous
}).responseText;
}
Otherwise you need to use showBids function as callback:
function playerid(playername, callback) {
$.ajax({
type: "POST",
url: "fn.php?playerid",
data: "playername="+playername,
success: function(data) {
callback(data);
}
});
}
//Usage
playerid(ui.item.value,showBids);

jQuery parallel AJAX call mixes up return values

In the following JavaScript code I repeatedly make AJAX calls to my FastCGI module to query some values. At some point the code terminates when the data variable for the div2 case is not 0 but contains the value that should go into div1 while the div1 displays the value that was supposed to go into div2.
I am using the Chromium Browser (14.0.835.202 (Developer Build 103287 Linux) Ubuntu 10.10) but it also happens with FireFox. I also tried using the XMLHttpRequest object alone and I got the same results.
How can this be and how can this be solved?
function TimerEvent() {
$.ajax({
url: "/cgi-bin/wvvar.cgi",
type: "POST",
data: "cmd=get&varname=s#SYSDATETIME",
success: function(data) {
document.getElementById("div1").innerHTML = data;
}
});
$.ajax({
url: "/cgi-bin/wvvar.cgi",
type: "POST",
data: "cmd=get&varname=#LOGINSTATE",
success: function(data) {
document.getElementById("div2").innerHTML = data;
if (data == "0")
setTimeout("TimerEvent()", 50);
}
});
}

Maybe try have them sequential:
function TimerEvent() {
$.ajax({
url: "/cgi-bin/wvvar.cgi",
type: "POST",
data: "cmd=get&varname=s#SYSDATETIME",
success: function(data) {
document.getElementById("div1").innerHTML = data;
$.ajax({
url: "/cgi-bin/wvvar.cgi",
type: "POST",
data: "cmd=get&varname=#LOGINSTATE",
success: function(data) {
document.getElementById("div2").innerHTML = data;
if (data == "0")
setTimeout("TimerEvent()", 50);
}
});
}
});
}

If your requirements allows, try this:
function TimerEvent() {
$.ajax({
url: "/cgi-bin/wvvar.cgi",
type: "POST",
data: "cmd=get&varname=s#SYSDATETIME",
success: function(data) {
document.getElementById("div1").innerHTML = data;
$.ajax({
url: "/cgi-bin/wvvar.cgi",
type: "POST",
data: "cmd=get&varname=#LOGINSTATE",
success: function(data) {
document.getElementById("div2").innerHTML = data;
if (data == "0")
setTimeout("TimerEvent()", 50);
}
});
}
});
}

Try to execute the calls synchronously by adding the async=false option.