This seems like an incredibly simple issue but I have no idea why I'm getting undefined. I'm using jQuery to fetch data off a PHP script - specifically a string which the PHP file echoes. Here's the code:
<script type="text/javascript">
var map1;
$.get("script.php", function(data)
{
map1 = data;
});
alert(map1);
</script>
Now if I alert(map1), it ends up being undefined... why exactly is this the case? I thought by declaring map1 outside $.get, it would fix the problem but that's not the case. If I alert(map1) inside the $.get function, it ends up fine and the variable holds a string (as opposed to being undefined). So the question is... what's going on with map1? And how can I stop it from being undefined / going out of scope / whatever is happening to it?
Thanks in advance.
Because your alert is executed before get finished. Put right after assignment in function body. get initiates the request and returns.
As #Michael has put, the .get call is asynchronous so your javascript is executing this call, and then carrying on with your script, which is why you get an undefined alert box.
Your best option is to put in a success call:
$.get("script.php", function(data)
{
map1 = data;
})
.success(function() { alert(map1); });
$.get runs asynchronously, and this is why the function's second parameter is an anonymous function. This anonymous function is invoked once $.get has finished executing. alert(map1) is invoked immediately, and not asynchronously. You could add the alert call to the anonymous function passed to $.get:
$.get("script.php", function(data){
map1 = data;
alert(map1);
});
Because your $.get fills the data slower than your alert is executed !
Which means your $.get function takes longer to compute than your alert !
You could use setTimeout() to work around this but I think its a bad practice.
What about doing it this way?
var map1;
$.ajax({
type: "GET",
url: "script.php",
async: true,
success : function(data)
{
map1 = data;
alert (data);
}
});
Related
On alert it always alerts jojo. The test2.php have text Loco
The div gets updated to Loco but the global variable is not changing. I tried window.temp = data but it didn't worked.
How can i get the returned value in variable? please Guide...
<div>
yolo
</div>
<script type="text/javascript">
var temp = 'jojo';
$.ajax({
url: 'test2.php', //Loco
success: function(data)
{
temp = data;
$('div').html(data);
},
error: function (err)
{
alert('error');
}
});
alert(temp);
var toBeUsedLater = temp; //updated temp value from ajax call
refreshTab();
</script>
This is an asynchronous function. (That's what the A in AJAX stands for.) You are alerting the value of temp immediately , so it is happening before the asynchronous call has finished. If you add
alert(temp);
To the end of your success handler, you will see the value has updated.
AJAX - asynchronous means you are not waiting for response to come and Javascript is interpreted language executed one line after another line. So here the alert(temp) would be executed first and then the success callback as it takes some time to get the response.
1)change
var temp = 'jojo'
to
'temp = 'jojo'
As this is not tied down to the execution context and not limited to files (has pluses and minuses - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/var
2) The problem is that the alert is called before the callback.
Move the alert into the function. As the ajax is called asynchronously, meaning the success and error functions are called, only when the ajax gets the response back from the server, while the alert you have now will be called right away.
http://javascript.about.com/od/ajax/a/ajaxasyn.htm
$.ajax({
url: 'test2.php', //Loco
success: function(data)
{
temp = data;
$('div').html(data);
alert(temp).
},
error: function (err)
{
alert('error');
}
});
3) alternatively you could set the async of the ajax to false:
What does "async: false" do in jQuery.ajax()?
Which will cause the Ajax call will finish before the next line of code, but it is highly recommended not to do that.
Just add async: false in your ajax options.
I'm having some problems with AJAX and the scope of my data. I am new to Javascript and I'm not sure how to fix my problem.
var urlList = new Array();
$.ajax({
url: "http://localhost:3000/url",
success: function(data) {
alert(data.expressions.url); //This shows the correct result
urlList[0] = obj.expressions.dom;
}
});
alert(urlList[0]); //this shows undefined
I need the data that is in urlList[0] so i can use it at a later time. I think it's a scope problem.
Could someone point me in the right direction please?
Thanks
It's not a scope problem, but a timing problem. The ajax method is executed asynchronously. That means that calling it will not cause your program to wait until it is finished. This results in the alert being shown before the request is finished.
To fix this, put the request inside the success function as well. This is the proper place to handle the results of the request.
var urlList = new Array();
$.ajax({
url: "http://localhost:3000/url",
success: function(data) {
alert(data.expressions.url); //This shows the correct result
urlList[0] = obj.expressions.dom;
// This might work now, depending on what `obj.expressions.dom` is. This
// isn't becoming clear from your code. Usually you would use the `data`
// parameter of the success function, which contains the response body of
// the ajax request that has just finished.
alert(urlList[0]);
// of course you can call other functions as well. For instance, you
// could call
urlListChanged();
// ..which you can declare in global scope. This way, you can repond to
// changes from multiple sources, without having to duplicate code.
// It will all work, as long as you use the success handler as the trigger.
}
});
function urlListChanged()
{
alert(urlList[0]);
}
Your problem is one of chronology.
$.ajax fires an asynchronous request, meaning the rest of your code after it will continue to be executed before the request has resolved. Since urlList is populated only once the request resolves, your alert is firing too early.
Change
$.ajax...
to
var req = $.ajax...
and wrap your alert in a success callback:
req.done(function() { alert(urlList[0]); });
...or just move the alert inside your existing success callback.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
How can I get jQuery to perform a synchronous, rather than asynchronous, AJAX request?
Get a variable after ajax done
The two alert functions in the following code returns different results. I am trying to get the second to evaluate true too.. Any help is appreciated.. Thanks..
var array;
$.get('php/getstocklist.php', function(data){
array = data;
alert($.isArray(array)); //alerts true
}, "json");
alert($.isArray(array)); //alerts false
The problem is that the $.get is async. The var is global as you have it now. It just isn't defined because your second alert runs immediately before the ajax has returned and run its success callback.
In order to use it outside the the callback you would need to poll a variable to make sure the result has been assigned... but then you are essentially using a fake callback so it makes more sense to restructure your code and do it the normal way :-)
Here's what's happening:
// This variable _is_ global. However, it's current value is undefined
var array;
$.get('php/getstocklist.php', function(data){
// After this runs, _now_ array has data in it
array = data;
// thus causing $.isArray to return true here.
alert($.isArray(array)); //alerts true
}, "json");
// This call happens BEFORE the callback to the $.get call,
// so as of this line, array is still undefined, which results in
// the $.isArray call returning false.
alert($.isArray(array)); //alerts false
Javascript is a heavy asynchronous language. You have to kind of break away from procedure thinking, and instead think in terms of passing bits of code around to be executed later (those are callbacks).
The second alert executes before the first because the $.get callback executes asynchronously. If you want the second alert to return true, you should use a jQuery Deferred object like so:
var array;
deferred = $.get('php/getstocklist.php', function(data){
array = data;
alert($.isArray(array)); //alerts true
}, "json");
// alerts true if $.get succeeded
deferred.done(function () { alert($.isArray(array)); });
The callback you pass to done will fire when the asynchronous $.get call returns.
If I understand you right why can't you
$.getJSON('php/getstocklist.php', function(data){
dosomething(data);
});
function dosomething(data) {}
Its a bit off a fudge but try setting using that will break your variable out off the request and make it global
window.array = data;
alert($.isArray(window.array));
I am having a problem, or perhaps a lack of understanding, with the jQuery execution order of $.get() function. I want to retrieve some information from a database server to use in the $.ready() function. As you all know, when the get returns, it passes the data to a return handler that does something with the data. In my case I want to assign some values to variables declared inside the ready handler function. But the problem is, the return handler of $.get() does not execute until after ready has exited. I was wondering if (a) am I doing this right/is there a better way or if (b) there was a way around this (that is, force the get return handler to execute immediately or some other fix I'm not aware of). I have a feeling this is some closure thing that I'm not getting about JavaScript.
As per request, I'll post an example of what I mean:
$(function() {
var userID;
$.get(uri, function(returnData) {
var parsedData = JSON.parse(returnData);
userID = parsedData.userID;
});
});
So as you can see, I'm declaring a variable in ready. Then using a get call to the database to retrieve the data needed. Then I parse the JSON that is returned and assign the userID to the variable declared before. I've tested it with a couple alerts. An alert after the get shows userID as undefined but then an alert in get's return handler shows it to be assigned.
$.get() is asynchronous. You have to use a callback to fill your variable and do the computation after the request is complete. Something like:
$(document).ready(function(){
$.get( "yourUrl", function( data, textStatus, jqXHR ) {
var myData = data; // data contains the response content
// perform your processing here...
registerHandlers( myData ); // you can only pass "data" off course...
});
});
// your function to register the handlers as you said you need to.
function registerHandlers( data ) {
// registering handlers...
}
$.get is an ajax request. A in AJAX stand for asynchronous, so script won't wait for this request to finish, but instead will proceed further with your code.
You can either use complete callback or you can use $.ajax and set async to false to perform synchronous request.
The $.get() function executes an async httprequest, so the callback function will be executed whenever this request returns something. You should handle this callback outside of $.ready()
Maybe if you explain exactly what do you want to do, it would be easier to help!
Are you looking for something like:
$(document).ready(function(){
var variable1, variable 2;
$.get('mydata.url', function(data){
variable1 = data.mydata1;
variable2 = data.mydata2;
});
});
If you declare the variables first, then you can set their values within the get call. You can add a function call at the end of the get handler to call a separate function using these values? Without some kind of example, its hard to go into any more detail.
Without seeing the full code, my guess is that you should declare your variable outside $.ready; initialize it in ready for the initial page load; then update it from the get callback handler.
for example
var x = ""; // declaration
$(document).ready(function() { x = "initial value"; });
$.get(...).success(function() { x = "updated from ajax"; });
I'm sure the solution is staring me right in the eyes, but I just cannot see it. I am trying to load an object from an outside file source. I've tried it several which ways using jQuery's built in methods, but keep returning undefined. Is my issue the scope? I need partnerData right where it is because of other dependent methods in my script. I don't want to operate the rest of my site's functions from within the $.get callback. Any help is greatly appreciated, here's the code:
$(function() {
var partnerData;
$.get('data/partners.json', function(file) {
partnerData = $.parseJSON(file);
});
console.log(partnerData); /* returns undefined instead of object */
});
EDIT:
Thanks for all the feedback everyone. This is the solution I went with:
var partnerData;
$.ajax({
url: 'data/partners.json',
dataType: 'json',
async: false,
success: function(data) {
partnerData = data;
}
});
The reason why you're seeing undefined is because ajax requests are asynchronous by default. This means your get method gets invoked and the code flow moves down to the next statement while the request executes in the background. Your callback function is later invoked when the request completes.
Using callback functions is a common pattern used in situations like this. But you seem to be saying you don't want to do or can't do that. In that case, you could use async: false which would force the request to be synchronous. Keep in mind however, that your code will be blocked on the request and if it's a long-lived request, the user experience will degrade as the browser will lock up.
P.S. You shouldn't need to parseJSON - if response has the correct mime-type set, jQuery will intelligently guess the type and parse the JSON automatically. And in case the server isn't sending back the correct mime-type, you can also explicitly tell jQuery what the expected return data type is; see the dataType argument to $.get() .
One way you might modify your code, to force synchronous requests:
$.ajax({
type: 'GET',
url: 'data/partners.json',
success: function(file){
partnerData = $.parseJSON(file);
//ideally you would perform a callback here
//and keep your requests asynchronous
},
dataType: 'json',
async: false
});
function is proccessed to the end event when ajax is still being proccessed. insert it into callback function
$(function() {
var partnerData;
$.get('data/partners.json', function(file) {
partnerData = $.parseJSON(file);
console.log(partnerData);
});
});
I would say that your problem is the same of the one that I just solved, if $.get is AJAX! and it is setting a variable, to read that variable outside the callback you need to wait the response! So you have to set async=false!
console.log in synchronous and get is async.
try:
$(function() {
var partnerData;
$.get('data/partners.json', function(file) {
partnerData = $.parseJSON(file);
test();
});
function test(){
console.log(partnerData);
}
});