I have an ajax call that might take a bit to complete. I don't want to use async:false because I want it to stay non blocking code. So I decided to use Q. The problem is I don't understand how ca I extract the json that came back from Q.when($.ajax...). I'm new to Q.
In this example I would like the variable to hold the json that came back from the server:
var res = Q.when($.ajax({
type: "POST",
url: "GetData.asmx/GetMembersList",
contentType: "application/json; charset=utf-8",
dataType: "json"
}));
return res;
With asynchronous calls you can't just assign the result to a variable, because that result won't exist until sometime in the future. Q.when does not return the result, it returns a promise object that will eventually resolve with a result.
If there is only ever one thing you want to do with the JSON you could just inline a .then call to get the result.
Q($.ajax({
type: "POST",
url: "GetData.asmx/GetMembersList",
contentType: "application/json; charset=utf-8",
dataType: "json"
})).then(function (res) {
// res now contains the JSON
});
However the real power of promises comes with the fact that you can pass them around and use them later.
function getMembersList() {
return Q($.ajax({
type: "POST",
url: "GetData.asmx/GetMembersList",
contentType: "application/json; charset=utf-8",
dataType: "json"
}));
}
var membersList = getMembersList();
membersList.then(function (res) {
// once the AJAX call completes this will
// run. Inside this function res contains the JSON
return res; // pass res to the next chained .then()
}).then(function (res) {
// you could chain another then handler here
});
// do some other stuff
membersList.then(function (res) {
// you could also add another then handler later too
// even long after the AJAX request resolved and this
// will be called immediately since the promise has already
// resolved and receive the JSON just like the other
// then handlers.
});
You don't need to use Q if you don't have other reasons for using it, since version 1.5 jQuery returns a deferred object from AJAX calls. A Deferred is similar to a promise. Q does offer more power and jQuery's promises/deferreds don't exactly implement the Promises/A standard, potentially causing problems with error handling. For something simple like an AJAX call jQuery promises are usually good enough if you are already using jQuery anyway.
var membersList = $.ajax({
type: "POST",
url: "GetData.asmx/GetMembersList",
contentType: "application/json; charset=utf-8",
dataType: "json"
});
membersList.then(function (res) {
// res now contains the JSON
});
Here are some examples from the q documentation about using with jQuery ajax.
return Q(jQuery.ajax({
url: "foobar.html",
type: "GET"
})).then(function (data) {
// on success
}, function (xhr) {
// on failure
});
// Similar to jQuery's "complete" callback: return "xhr" regardless of success or failure
return Q.promise(function (resolve) {
jQuery.ajax({
url: "foobar.html",
type: "GET"
}).then(function (data, textStatus, jqXHR) {
delete jqXHR.then; // treat xhr as a non-promise
resolve(jqXHR);
}, function (jqXHR, textStatus, errorThrown) {
delete jqXHR.then; // treat xhr as a non-promise
resolve(jqXHR);
});
});
https://github.com/kriskowal/q/wiki/Coming-from-jQuery
Hope that helps.
Related
I've got a small javascript function that's only purpose is to call a script to get some data from the database so it can be used by other functions on the client side.
I'm using a jQuery call to get the data but for me to pass the object out of the success functions scope I need to turn asynchronous off which raises a deprecation warning.
My function works as intended currently but I'd like to use a method that isn't deprecated. Here is my function:
function getData(ID) {
var Data = {};
$.ajax({
url: 'script',
method: 'POST',
dataType: 'json',
async: false,
data: {action: 'get', id: ID },
success: function(response) {
Data = response;
})
});
return Data;
}
I've changed the variable names for privacy reasons so apologies if they're vague.
Also why is synchronous calls considered harmful to the end users experience?
As AJAX call is asynchronous, you will always get blank object ({}) in response.
There are 2 approach.
You can do async:false
To get response returned in AJAX call try like below code. Which wait for response from server.
function getData(ID) {
return $.ajax({
url: 'script',
method: 'POST',
dataType: 'json',
//async: true, //default async call
data: {action: 'get', id: ID },
success: function(response) {
//Data = response;
})
});
}
$.when(getData(YOUR_ID)).done(function(response){
//access response data here
});
I'm trying to add another asynchronous call to the contract of an existing Deferred before its state is set to success. Rather than try and explain this in English, see the following pseudo-code:
$.when(
$.ajax({
url: someUrl,
data: data,
async: true,
success: function (data, textStatus, jqXhr) {
console.log('Call 1 done.')
jqXhr.pipe(
$.ajax({
url: someUrl,
data: data,
async: true,
success: function (data, textStatus, jqXhr) {
console.log('Call 2 done.');
},
})
);
},
}),
$.ajax({
url: someUrl,
data: data,
async: true,
success: function (data, textStatus, jqXhr) {
console.log('Call 3 done.');
},
})
).then(function(){ console.log('All done!'); });
Basically, Call 2 is dependent on the results of Call 1. I want Call 1 and Call 3 to be executed in parallel. Once all 3 calls are complete, I want the All Done code to execute. My understanding is that Deferred.pipe() is supposed to chain another asynchronous call to the given deferred, but in practice, I always get Call 2 completing after All Done.
Does anyone know how to get jQuery's Deferred to do what I want? Hopefully the solution doesn't involve ripping the code apart into chunks any further.
Thanks for any help.
UPDATE: Please see my follow up question.
You have to call .pipe on the deferred object returned by the first $.ajax call, not inside its success callback (this does not have any effect at all):
$.when(
$.ajax({
// ...
}).pipe(function() {
// return a deferred object from .pipe
return $.ajax({
// ...
});
}),
$.ajax({
// ...
})
).done(function(){ console.log('All done!'); });
.pipe returns a new deferred object which only gets resolved once both, the original deferred object and the returned one get resolved.
Hi I have 2 ajax calls in my script, I need them run asnyc to spare time, but I need the second to wait until the first is finished.
$.ajax({
type: "POST",
url: "getText.asmx/ws_getText",
data: parO1,
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function (msg) {
alert(msg.d.data);
},
error: function () {
chyba("chyba v požadavku", "df");
}
});
if (parO2.length > 0) {
$.ajax({
type: "POST",
url: "getText.asmx/ws_getText",
data: parO2,
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function (msg) {
/*WAIT UNTIL THE FIRST CALL IS FINISHED AND THAN DO SOMETHING*/
},
error: function () {
chyba("chyba v požadavku", "df");
}
});
}
So any ideas? Thanks
If using jQuery 1.5+, you can use jQuery.when() to accomplish this. Something like (shortened the ajax calls for brevity, just pass the objects as you're doing above)
$.when($.ajax("getText.asmx/ws_getText"),
$.ajax("getText.asmx/ws_getText")).done(function(a1, a2){
// a1 and a2 are arguments resolved for the
// first and second ajax requests, respectively
var jqXHR = a1[2]; // arguments are [ "success", statusText, jqXHR ]
});
You don't know in which order they will return so if you were rolling this by hand, you would need to check the state of the other request and wait until it has returned.
You need to wire up the second call to be contained within the callback of your first ajax call. Like so:
success: function(msg)
{
alert(msg.d.data);
if(par02.length > 0)
{
// Your 2nd ajax call
}
},
Since JavaScript doesnt run in multiple threads on the client, you can't block the thread until certain conditions are met.
Using jquery
$.ajax({
type: "POST",
async:false, // ** CHANGED **
url: "getText.asmx/ws_getText",
data: parO1,
contentType: "application/json; charset=utf-8",
dataType: "json",
success: function (msg) {
alert(msg.d.data);
}
, error: function () {
chyba("chyba v požadavku", "df");
}
});
Here is another answer on running dual ajax requests. Like Tejs, the user makes an ajax call within the success method...
The poster states You're better off having the success method launch a new ajax request.."
Having two $.ajax() calls in one script
I have a strange (probably not for some I would wager) problem, I have a JavaScript method to call all of my ajax calls, please see below.
function ajaxCall(url, params) {
if (params === null) {
$.ajax({
type: 'POST',
url: url,
contentType: 'application/json; charset=utf-8',
dataType: 'json'
}).success(function(response) {
return response;
}).error(function(response) {
return response;
});
} else {
var data = JSON.stringify(params);
$.ajax({
type: 'POST',
url: url,
data: data,
contentType: 'application/json; charset=utf-8',
dataType: 'json'
}).success(function(response) {
return response;
}).error(function(response) {
return response;
});
}
}
when I call this method I get the appropriate response from the AJAX call and all looks rosy, until I return the response the call is returned undefined?
for completeness I will include my call code.
var call = ajaxCall(someUrl, someParams);
just to clarify and make sure my ramblings are understood call would be undefined in the above example?
you can't do that because the ajax call is async,
$.ajax returns a Deferred Object and you can work with it to get what you need
read on it here
the ajax call is async by nature and dosent return anything. so when you do something like this
var call = ajaxCall(someUrl, someParams);
then a request is sent to the server and next lines begins to execute. without putting the value in the call variable;
also code like this
.success(function(response) {
return response;
would do nothing as .success() takes a function or rather a callback to execute when the response is successfull so if u return something in this and put the async flag in the $.ajax() options to true. then also nothing/undefined will be returned.
I am trying to implement Repository pattern in JavaScript. I have ViewModel which i want to initialize with the data when i call Initialize method on it. Everything seems to be falling in places except that i am not able to return the data from my AJAX call. I can see that data is coming back from the ajax call but when i trying to capture the data in SomeViewModel's done function, it is null.
Can someone please point me out where i am going wrong here?
P.S: Please notice that i am not making Async call so the call chain is properly maintained.
This is how my Repository looks like:
function SomeRepository(){
this.LoadSomeData = function loadData()
{
$.ajax({
type: "POST",
url: "someUrl",
cache: true,
async: false,
contentType: "application/json; charset=utf-8",
data: "{}",
dataType: "json",
//success: handleHtml,
success: function(data) {
alert('data received');
return data;
},
error: ajaxFailed
});
function ajaxFailed(xmlRequest) {
alert(xmlRequest.status + ' \n\r ' +
xmlRequest.statusText + '\n\r' +
xmlRequest.responseText);
}
}
};
This is how my ViewModel looks like:
function SomeViewModel(repository){
var self = this;
var def = $.Deferred();
this.initialize = function () {
var def = $.Deferred();
$.when(repository.LoadSomeData())
.done(function (data) {
def.resolve();
});
return def;
};
}
This is how i am calling from an aspx page:
var viewModel = new SomeViewModel(new SomeRepository());
viewModel.initialize().done(alert('viewmodel initialized'));
alert(viewModel.someProperty);
I have used successfully an auxiliar variable to put the ajax result, when ajax call is inside a function (only works if ajax is async=false) and i need the function does return the ajax result. I don't know if this is the best solution.
function ajaxFunction(){
var result='';
$.ajax({
type: "POST",
url: "someUrl",
cache: true,
async: false,
contentType: "application/json; charset=utf-8",
data: "{}",
dataType: "json",
//success: handleHtml,
success: function(data) {
alert('data received');
result=data;
},
error: ajaxFailed
});
return result;
}
Doesn't matter that it's synchronous (though it really shouldn't be). Returning a value from inside the ajax callback will not cause the value to be returned from the containing function.
Using asynchronous ajax is generally a much better idea anyway, but that will force you to create an API that allows its clients to pass in handlers to be called when the ajax request completes. To do that, you'd give your "LoadSomeData" function a parameter. A caller would pass in a function, and your ajax "success" handler would pass on the results (or some transformation of the results; depends on what it is that you're doing) to that callback. It's the same idea as the callbacks used in the ajax call itself.