I'm having a problem with something that is likely a simple error.
As you will notice below, I have a check for duplicate function that references external PHP checking a database. The PHP is working, and returning data.
When I use duplicationCheck.done() and parse the data, my if statement responds correctly (i.e., if the user has entered a duplicate, this checks that. HERE'S the issue: Despite my if statement below functioning correctly, when isDuplicate is set to true, it appears as undefined when the console.log command is called below the done() function. I can't figure out why. With my research, I think that it is a problem with the async nature of the AJAX call?
Thank you for your time. Any ideas?
$("#username_submit").click(function() {
function checkForDuplication(username) {
return $.ajax({
url: 'static/experiments/computerized_handwriting/random_assignment.php',
type: 'POST',
data: {userName: username}
});
}
var duplicationCheck = checkForDuplication($('input:text').val());
var isDuplicate;
duplicationCheck.done(function(data){
var response = JSON.parse(data);
if(response.data['json_array'] == "duplicate"){
isDuplicate = true;
alert("dup");
} else {
isDuplicate = false;
}
});
console.log(isDuplicate);
....
This is due to the asynchronous nature of ajax.
You need to check for the duplication once it returns from the server in the done function.
But your duplicationCheck variable is not a reference to the function, but what it is returning.
The proper way would be like this:
$("#username_submit").click(function() {
$.ajax({
url: 'static/experiments/computerized_handwriting/random_assignment.php',
type: 'POST',
data: { userName: $('input:text').val()}
}).done(function() {
var response = JSON.parse(data);
if (response.data['json_array'] == "duplicate") {
isDuplicate = true;
alert("dup");
}
else {
isDuplicate = false;
}
console.log(isDuplicate);
});//done
});//submit click
....
Related
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
}
});
}
Updated Question with Code
I have a situation where I am calling two nested ajax calls one after another. The first ajax call submits a form without the attachment. The result of the first ajax call will create a requestId and using second ajax call I have to attach multiple attachments to the created requestId.
The result of below code, both first and second ajax calls are being called N times of attachment. For ex:- If there are 3 attachments, createRequestId ajax call(first ajax call) called 3 times which creates 3 requestIds. My issue is, createRequestId ajax call needs to be called only one time (first time) and during rest of the loop, only the second ajax call should be called. How can I achieve this in the below code?
Current situation
RequestId 1,Attachment 1
RequestId 2,Attachment 2
RequestId 3, Attachment 3
Expected output
RequestId 1, Attachment 1, Attachment 2, Attachment 3
//loop through number of attachments in the form
$("#myDiv").find("input[type=file]").each(function(index,obj) {
var fObj = $(obj),
fName = fObj.attr("name"),
fileDetail = document.getElementById(fName).files[0];
//FileSize Validation
if(fileDetail !=undefined && fileDetail !=null)
{
if(fileDetail.size > 5*Math.pow(1024,2))
{
alert("Please upload the attachment which is less than 5 MB");
return false
}
}
$.ajax({ //First Ajax Call
url: 'http://..../createRequestId'
type:'POST'
data: stringify(formData)
success: function(resObj){
$("#showResponseArea span").removeClass("hide");
$("#showResponseArea span").removeClass("alert-success");
var requestId = resObj.requestId;
if(requestId>1 && fileDetail !=undefined && fileDetail !=null) {
$.ajax({ //Second Ajax Call
url: 'http://..../doAttach?fileName=' + fileDetail.name +
'&requestId=' +requestId,
type:'POST',
data: fileDetail,
success: function(resObj){
alert("Attachment Successful");
}
error : function(data) {
alert("Failed with the attachment");
}
});
}
},
error: funciton(resObj) {
alert("Some Error Occured");
}
});
});
I know this doesn't really answer your question in full, but if you don't mind me offering a little constructive code review. It's hard to really manage and debug code when it's all thrown into one big function with many lines, especially if you're nesting async calls (you're getting close to nested callback hell). There's a reason code like this can get hard to maintain and confusing.
Lets incorporate some Clean Code concepts which is to break these out into smaller named functions for readability, testability, and maintainability (and able to debug better):
First you don't need all those !== and undefined checks. Just do:
if (fileDetail)
and
if(requestId>1 && fileDetail)
that checks for both null and undefined on fileDetail.
Then I’d start to break out those two ajax calls into several named functions and let the function names and their signatures imply what they actually do, then you can remove unnecessary comments in code as well as once you break them out, typically you can find repeated code that can be removed (such as redundant post() code), and you will find that code you extracted out can be tested now.
I tend to look for behavior in my code that I can try to extract out first. So each one of those if statements could easily be extracted out to their own named function because any if statement in code usually translates to "behavior". And as you know, behavior can be isolated into their own modules, methods, classes, whatever...
so for example that first if statement you had could be extracted to its own function. Notice I got rid of an extra if statement here too:
function validateFileSize(fileDetail)
if(!fileDetail && !fileDetail.size > 5*Math.pow(1024,2)){
alert("Please upload the attachment which is less than 5 MB");
return false
};
};
So here's how you could possibly start to break things out a little cleaner (this could probably be improved even more but here is at least a start):
$("#myDiv").find("input[type=file]").each(function(index,obj) {
var fObj = $(obj),
fileName = fObj.attr("name"),
file = document.getElementById(fileName).files[0];
validateFileSize(file);
post(file, 'http://..../createRequestId');
});
// guess what, if I wanted, I could slap on a test for this behavior now that it's been extracted out to it's own function
function validateFileSize(file){
if(!file && !file.size > 5*Math.pow(1024,2)){
alert("Please upload the attachment which is less than 5 MB");
return false
};
};
function post(url, data){
$.ajax({
url: url,
type:'POST',
data: stringify(data),
success: function(res){
showSuccess();
var id = res.requestId;
if(id > 1 && file){
var url = 'http://..../doAttach?fileName=' + file.name + '&requestId=' + id;
postData(file, url);
}
},
error: function(err) {
alert("Some Error Occurred: " + err);
}
});
// I didn't finish this, and am repeating some stuff here so you could really refactor and create just one post() method and rid some of this duplication
function postData(file, url){
$.ajax({
url: url,
type:'POST',
data: file,
success: function(res){
alert("Attachment Successful");
},
error : function(data) {
alert("Failed with the attachment");
}
});
};
// this is behavior specific to your form, break stuff like this out into their own functions...
function showSuccess() {
$("#showResponseArea span").removeClass("hide");
$("#showResponseArea span").removeClass("alert-success");
};
I'll leave it here, next you could get rid of some of the duplicate $ajax() code and create a generic post() util method that could be reused and move any other behavior out of those methods and into their own so that you can re-use some of the jQuery ajax call syntax.
Then eventually try to incorporate promises or promises + generators chain those async calls which might make it a little easier to maintain and debug. :).
I think your loop is simply in the wrong place. As it is, you're iterating files and making both AJAX calls once.
Edit: I now show the appropriate place to do extra validations before the first AJAX call. The actual validation was not part of the question and is not included, but you can refer to JavaScript file upload size validation.
var fileSizesValid = true;
$("#myDiv").find("input[type=file]").each(function(index, obj) {
// First loop checks file size, and if any file is > 5MB, set fileSizesValid to false
});
if (fileSizesValid) {
$.ajax({ //First Ajax Call
url: 'http://..../createRequestId',
type: 'POST',
data: stringify(formData),
success: function(resObj) {
var fObj = $(obj),
fName = fObj.attr("name"),
fileDetail = document.getElementById(fName).files[0];
//loop through number of attachments in the form
$("#myDiv").find("input[type=file]").each(function(index, obj) {
$("#showResponseArea span").removeClass("hide");
$("#showResponseArea span").removeClass("alert-success");
var requestId = resObj.requestId;
if (requestId > 1 && fileDetail != undefined && fileDetail != null) {
$.ajax({ //Second Ajax Call
url: 'http://..../doAttach?fileName=' + fileDetail.name +
'&requestId=' + requestId,
type: 'POST',
data: fileDetail,
success: function(resObj) {
alert("Attachment Successful");
},
error: function(data) {
alert("Failed with the attachment");
}
});
}
})
},
error: function(resObj) {
alert("Some Error Occured");
}
});
}
As a side note, take care where you place your braces. In JavaScript your braces should always be at the end of the line, not the start. This is not a style preference thing as it is most languages, but an actual requirement thanks to semicolon insertion.
Try following code (Just a re-arrangement of your code and nothing new):
//loop through number of attachments in the form
var requestId;
$("#myDiv").find("input[type=file]").each(function(index,obj) {
var fObj = $(obj),
fName = fObj.attr("name"),
fileDetail = document.getElementById(fName).files[0];
//FileSize Validation
if(fileDetail !=undefined && fileDetail !=null)
{
if(fileDetail.size > 5*Math.pow(1024,2))
{
alert("Please upload the attachment which is less than 5 MB");
return false
} else if(!requestId || requestId <= 1){
$.ajax({ //First Ajax Call
url: 'http://..../createRequestId'
type:'POST'
data: stringify(formData)
success: function(resObj){
$("#showResponseArea span").removeClass("hide");
$("#showResponseArea span").removeClass("alert-success");
requestId = resObj.requestId;
secondAjaxCall(fileDetail);
},
error: funciton(resObj) {
alert("Some Error Occured");
}
});
} else if(requestId>1) {
secondAjaxCall(fileDetail);
}
}
});
function secondAjaxCall(fileDetail) {
$.ajax({ //Second Ajax Call
url: 'http://..../doAttach?fileName=' + fileDetail.name +
'&requestId=' +requestId,
type:'POST',
data: fileDetail,
success: function(resObj){
alert("Attachment Successful");
}
error : function(data) {
alert("Failed with the attachment");
}
});
}
I have this problem when I use setInterval and ajax for retrieving data from the database and if the data that I retrieve from the database is equal to saveHere then it will loop again until it does not match the variable saveHere, it freeze the browser until the data that I retrieve is not equal to saveHere.
Here is an example:
var saveHere = 'RED';
var interval = setInterval(function() {
var sample = $.ajax({
type: 'GET',
url: 'database.php',
data : data
}).responseText;
if (sample != 'RED') {
clearInterval(interval);
saveHere = sample;
}
else {
console.log('load again');
}
},1000);
I really need advice. Thank you in advance. Sorry for the grammar.
$.ajax is asynchronous and requires you to use a callback to get the response text.
Take a look at the documentation at http://api.jquery.com/jQuery.ajax/
What you want to do is to add a success parameter. Something like this:
var saveHere = 'RED';
doAjax();
function doAjax() {
$.ajax({
type: 'GET',
url: 'database.php',
data: data,
success: function (sample) {
if (sample != 'RED') {
saveHere = sample;
} else {
console.log('load again');
doAjax();
}
}
});
}
Notice how I've removed setInterval and instead wrapped the Ajax code in a function. The success callback will be called when the Ajax query has successfully finished, and give you the response. Once we have evaluated the response, we can run the doAjax function again to run the query again.
Without knowing the exact scenario, or what you're looking to achieve, I'd say the way you're going about your AJAX calls is very dangerous as it has the potential to constantly make a request every second, regardless of whether the server has had a chance to respond yet.
I'd be tempted to only make one request at a time, something like:
var saveHere = 'RED';
makeAjaxCall();
function makeAjaxCall() {
var url = 'database.php';
var data = {};
$.get(url, data, function(response_text){
if (response_text != 'RED')
{
saveHere = response_text;
// do whatever else you need...
}
else
{
// make another call...
console.log('calling again...');
makeAjaxCall();
}
}, "text");
}
You are clearing interval that means no interval will occur after that.
Instead what you can do is wrap interval inner code inside if condition as below.
var interval = setInterval(function()
{
if(sample != 'RED') {
var sample = $.ajax({
type: 'GET',
url: 'database.php',
data : data
}).responseText;
saveHere = sample;
}
else
{
console.log('load again');
}
},1000);
In your code you test for not equal to 'RED'.
if(sample != 'RED'){ . . .
That part of the loops stops the interval
If it doesn't equal red
}else{
It simple logs 'load again' without clearing the interval
What exactly are you trying to achieve ?
All I need is a method that returns true if the Url is responding. Unfortunately, I'm new to jQuery and it's making my attempts at writing that method rather frustrating.
I've seen several examples of jQuery using .ajax, but the code is consistently failing on me. What's wrong?
var urlExists = function(url){
//When I call the function, code is still executing here.
$.ajax({
type: 'HEAD',
url: url,
success: function() {
return true;
},
error: function() {
return false;
}
});
//But not here...
}
That isn't how AJAX works. AJAX is fundamentally asynchronous (that's actually what the first 'A' stands for), which means rather than you call a function and it returns a value, instead you call a function and pass in a callback, and that callback will be called with the value.
(See http://en.wikipedia.org/wiki/Continuation_passing_style.)
What do you want to do after you know whether the URL is responding or not? If you intended to use this method like this:
//do stuff
var exists = urlExists(url);
//do more stuff based on the boolean value of exists
Then what you instead have to do is:
//do stuff
urlExists(url, function(exists){
//do more stuff based on the boolean value of exists
});
where urlExists() is:
function urlExists(url, callback){
$.ajax({
type: 'HEAD',
url: url,
success: function(){
callback(true);
},
error: function() {
callback(false);
}
});
}
urlExists() can not return because it needs wait for the request.
Either pass it a callback, or make it synchronous (not recommended, because it locks the browser).
var urlExists = function(url, callback) {
if ( ! $.isFunction(callback)) {
throw Error('Not a valid callback');
}
$.ajax({
type: 'HEAD',
url: url,
success: $.proxy(callback, this, true),
error: $.proxy(callback, this, false)
});
};
Then you can do
urlExists('/something', function(success) {
if (success) {
alert('Yay!');
} else {
alert('Oh no!');
}
});
It also worth mentioning the same origin policy.
Also, returning from an anonymous function's scope will not return in the parent function (like in your original example). It just returns that inner function. To return from an inner to a parent, set a flag and return it.
Basically, there is nothing wrong with your code. See it work here:
http://jsfiddle.net/PK76X/
My guess is that you're using it to check the availability of content on a different domain, which fails because browsers don't allow cross domain ajax-requests.
If the url is from the same domain as your page you can do it. But if it is from a different domain, for example google.com, then it will fail due to cross domain security.
In general, you should probably run your script in Firefox using the firebug plugin. It will give you the details needed to solve the issue.
The ajax and post methods are asynchronous, so you should handle the result in a callback method.
AJAX is basically asynchronous, and that's why the behavior you are describing.
I've used the following, which is free of cross origin, to get a simple true/false indication whether a URL is valid, in a synchronous manner:
function isValidURL(url) {
var encodedURL = encodeURIComponent(url);
var isValid = false;
$.ajax({
url: "http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20html%20where%20url%3D%22" + encodedURL + "%22&format=json",
type: "get",
async: false,
dataType: "json",
success: function(data) {
isValid = data.query.results != null;
},
error: function(){
isValid = false;
}
});
return isValid;
}
The usage is then trivial:
var isValid = isValidURL("http://www.wix.com");
alert(isValid ? "Valid URL!!!" : "Damn...");
Hope this helps
Got some basic problem again.
I need to modify a function that previously returned a in code written object.
Im now trying to get the object from json through $.getJSON
function getEventData() {
var result = '';
$.getJSON("ajax.php?cmd=getbydate&fromdate=&todate=", function(data) {
result = data;
});
return result;
}
Problem is that result isn't set in the callback function for obvious reasons.
Do you guys have a solution for this?
Edit:
Ok i got an answer that was removed.
I just had to change it abit..
This is the answer that works:
function getEventData() {
var result = '';
url = "ajax.php?cmd=getbydate&fromdate=&todate=";
$.ajax({
url: url,
async: false,
dataType: 'json',
success: function(data) {
result = data;
}
});
return result;
}
You should program your application in an asynchronous way, which means, that you should use callback functions for you application flow, too, or continue in the getJson callback function. You can also make the request synchronously which should then be able to return the value (or at least assign it and block the function till the callback is completed), but this is not recommended at all:
function getEventData() {
var result = '';
result = $.ajax({
url: "ajax.php?cmd=getbydate&fromdate=&todate=",
async: false,
dataType: "json",
data: data,
success: function(data) {
return data;
}
});
return result;
}
Are you sure that the server returns valid json? It will be better to validate it using a tool like jsonlint. Also make sure that application/json is used as content type for the response.