This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 6 years ago.
I'm doing a GET request with jQuery inside of a function and trying to set a variable declared earlier in that function with the result. However, it comes up as undefined. Am I missing the concept here? How can I make something like this work? Thanks.
function doSomething1() {
var x;
$.get( window.location.href, { q: 'stuff', q2: $('input').val() }, function(data){
// value shows up
console.log(data);
x = data;
});
return x;
}
function doSomething2() {
// comes up as undefined.
console.log(doSomething1());
}
doSomething2();
This is a fault of the asynchronous effect of $.get() requests. You are returning x before the get has a chance to do anything. It takes a while to wrap your head around async functions.
The order of events is as follows:
doSomething2() calls doSomething1()
doSomething1() defines x without a value begins the GET request, and returns undefined.
doSomething2() logs the returned x value
The GET request finishes and processes its success function
Related
This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 8 years ago.
I have this code
var base_url = 'http://api.zxc.loc';
var questions = [];
function get_question(){
if(!questions.lenght){
$.get(base_url + '/api/questions', function(data){
questions = data;
console.log('get_question', questions); // GOOD, return [Object, Object ... etc ... ]
}, 'json')
}
console.log('get_question_2', questions); // BAD return empty array []
/* var question = questions[0];
delete questions[0];
return question; */
}
How you can see, in $.get questions variable not empty, but after $.get, questions is empty!
Why? Thanks
This is how AJAX works. In your code get_question_2 will be logged before get_question. Once an ajax call is made, the code proceeds past it (to get_question_2). Then one the ajax call is returned, the code inside your function (namely get_question) will be executed.
To summarize, the log with get_question_2 is being called as soon as the ajax call is finished being made and BEFORE the ajax call returns with the data.
This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 9 years ago.
Im having an issue assigning a string to a variable and then returning it. It sounds simple and should be but im completely lost as to why what is happening is happening.
My code:
function drawpills() {
var picid;
$.post('js/fetchdata.php', function (data) {
var clock = document.getElementById('clock');
clock.innerHTML = "<img src='images/clock/pill.png' alt='pill_image' id='pillpic" + data + "'/>";
picid = "pillpic" + data;
alert(picid); //if i run it here i get pillpic31 which is what i want
});
alert(picid); //if i run it here i get undefined which is not what i want and which is what is being returned
return picid;
}
I highlighted the issue with comments on the respective line. Any help is appriecated.
Suggest you read through the linked article in comments.
What you need is something like this:
function drawpills(callback){
var picid;
$.post('js/fetchdata.php', function(data){
var pcid = data; // process pcid here
callback(pcid);
});
}
The problem is the asynchronous behavior of AJAX. When the AJAX response is sent, it moves onto the next statement, whether or not the call has finished executing. You can now do one of two things. You could either make the AJAX synchronous, which will probably break the timing of events on the page, or you could create a callback to be executed when the AJAX call is completely finished.
$.post callback is asynchronous function,so:
function drawpills(){
var picid;
var callback = function(data){
var clock = document.getElementById('clock');
clock.innerHTML="<img src='images/clock/pill.png' alt='pill_image' id='pillpic"+data+"'/>";
picid="pillpic"+data;
alert(picid);
}
$.post('js/fetchdata.php', callback);
//picid is undefined,because callback is running until server response data.
//unless you using synchronous request
alert(picid);
return picid;
}
This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Closed 9 years ago.
I'm trying to use $.get() to retrieve data from a server, and assign it to a variable to work with it. For example:
$.get('htmllink', {}, function(results){
//do stuff here
});
var morestuff = ; //$.get() data goes here
The problem is, I can't get anything to work outside the rounded brackets. Everything is treated as internal variables or something. What am I missing?
You need to do all of your processing inside the callback function. This is because the call to $.get only starts an asynchronous request, and then the next line (var morestuff = ...) is executed after the request starts, but before it has completed.
$.get('htmllink', {}, function(results){
//do stuff with results in here
});
The problem here is that the $.get request is asynch (Ajax), so there is a timing issue here. The
var morestuff =
will run before the Ajax call returns, so you won't have the value to assign.
You have to interact with the result of the ajax request in the call back to have access to it
$.get('htmllink', {}, function(results){
//all code that depends on results must run inside here
});
//you can't execute code here that depends on the Ajax call
This question already has answers here:
How to return AJAX response Text? [duplicate]
(2 answers)
How do I return the response from an asynchronous call?
(41 answers)
Closed 9 years ago.
In the following code the alert inside the function works fine, but the second has variable undefined, and yet I have delcared the variable outside of the function. Why is this?
var data = [];
$.post(
'matchEngine.php',
function(data) {
for (var i = 0, len= data.length;i <len; i++) {
for ( h = 0, len2= data[i].length;h <len2; h++) {
data[i][h][0]=(data[i][h][0])*30;
data[i][h][1]=(data[i][h][1])*30;
data[i][h][3]=data[i][h][3].replace(/\"/,"");
}
}
alert(data[0][0][0]);
}
);
alert(data[0][0][0]);
if you are suffering a similar problem the following How to return the response from an AJAX call? has the definitive explanation and answer.
The reference data in the function parameter and outside the function are different variables. In first case, it is in global scope, and in the second it in the local scope..They are completely different.
The example illustrates the issue....
var data=2;//this
function fun(data){ //and this are different
alert(data);
}
var data2=3;
fun(data2);
You can try this:
var data = [];
var myRequest = $.post(
/* your stuff */
);
myRequest.done(function() { alert(data[0][0][0]); })
As pinkpanther noted, the local data variable inside your $.post callback is not the same variable as the data variable outside the function.
Additionally, since $.post is asynchronous, you need to either pass it a callback or use the deferred object that it returns to access the response.
$.post('matchEngine.php').then(function(data){alert(data)})
for example, if you want to be able to pass the response around to other functions, you can do something like:
function doPost(url){
return $.post(url);
}
function processResponse(response) {
alert(response);
}
responsePromise = doPost("matchEngine.php");
responsePromise.then(processResponse);
As an aside, I recommend using $.ajax instead of $.post if you are going to use the callback style instead of promises. The reason being that $.ajax provides an error callback while $.post does not.
This question already has answers here:
How do I return the response from an asynchronous call?
(41 answers)
Variable doesn't get returned from AJAX function
(2 answers)
JavaScript asynchronous return value / assignment with jQuery [duplicate]
(2 answers)
Closed 8 years ago.
I have the following method in JavaScript:
function getData(){
var result;
$.getJSON("app/data/ptl", function (data) {
if (data == null) {
return false;
}
var x_data = new Array();
var y_data = new Array();
$.each(data, function(index, value) {
x_data.push(index);
y_data.push(value);
});
result = [months_data,value_data];
});
alert('');
return result;
}
When this method is called, the exact data is retrieved. However when I remove alert('') the data is not received. Does anyone know a reasonable explanation for such problem?
That's because your function is asynchronous, and removing the alert makes the return r line being executed before the distant server answers.
You can't simply synchronously return from a function calling an asynchronous work. The usual solution is to provide a callback and execute what you want to do in the callback :
function fetchData(doWithData){
$.getJSON("app/data/ptl", function (data) {
if (data == null) {
return;
}
var x_data = new Array();
var y_data = new Array();
$.each(data, function(index, value) {
x_data.push(index);
y_data.push(value);
});
r = [months_data,value_data];
doWithData(r);
});
}
fetchData(function(result) {
// use result here
});
Your alert() and the return r; are OUTSIDE of the 'success' handler of your ajax call. Remember the AJAX calls are asynchronous. The alert forces the browser to wait for you to acknowledge the alert, which allows (usually) the AJAX call to complete and populate your r vairable. Without the alert, the .getJSON() returns immediately, BEFORE r is populated.
The $.getJSON() call sets up an asynchronous process. The function itself returns immediately (almost), but the callback function you pass in will be executed later, when the browser has actually received a response from the server you're contacting. Thus, it inherently makes no sense to return a value from such a callback, as nothing can or will pay attention to it.
Instead, you should do any work that requires access to the retrieved information inside the callback function.