How do you write a function that returns a value fetched from server via $.get?
This is what I have tried, which does not work:
function getMessage(key) {
$.get("/messages.json", function(data) {
return data.messages[key];
}, "json");
}
Any ideas?
Because Ajax requests are asynchronous. That is why you have to pass a callback to $.get, to handle the data once it is available. But the getMessage function returns before the $.get callback is executed.
You have to pass a callback that is doing something with the return value. E.g.:
function getMessage(key, cb) {
$.get("/messages.json", function(data) {
cb(data.messages[key]);
}, "json");
}
getMessage('foo', function(data) {
alert(data);
});
Of course you can also pass the callack directly to $.get and handle the data extraction there:
function getMessage(cb) {
$.get("/messages.json", cb);
}
There are two ways to handle this: use a synchronmous call via $.ajax or pass in a callback to your function instead of having it return a value. The latter is the canonical way to deal with AJAX since it retains the asynchronous nature of the call.
Asynchronous
function processMessage(key,elem,cb) {
$.get('/messages.json', function(data) {
if (cb && typeof(cb) === 'function') {
cb.apply(elem,data.messages[key]);
}
}
}
$('.something').each( function() {
processMessage('somekey', this, function(msg) {
$(this).append(msg);
});
});
Synchronous - try not to do it this way, since you'll lock your browser until it's done.
function getMessage(key)
{
var result = '';
$.ajax({
url: '/messages.json',
aSync: false,
type: 'get',
dataType: 'json',
success: function(data) {
result = data.messages[key];
}
});
return result;
}
$('.something').each( function() {
var msg = getMessage('somekey');
$(this).append(msg);
});
Note: these are untested.
Related
I am trying return callback value outside callback function example:
I make the function based in topic: How do I return the response from an asynchronous call?
(function (){
return getAjaxResult(function(result) { return result; });
//<-- Return Undefined (in console log return correct value)
})();
function getAjaxResult(callback){
$.ajax({
url: 'myurl',
type: 'GET',
success: function (result)
{
if (result === 'working'){
callback(result);
}else if (result === 'notworking'){
callback('notworking');
}
}
})
}
Return "Undefined" (in console log return correct value).
I do not know if this is the best option to return an ajax value in callback
There are two ways to do this, you can use async false but is deprecated and you can always use a promise:
do a function like this:
function ajaxCallback(id){
return $.ajax({
method: "POST",
url: "../YourUrl",
data: { id: id}
})
}
then call it like this:
if (id != '')//
{
ajaxCallback(id)
.done(function( response ) {
//do something with your response
});
}
Hope it helps
I have over 50 AJAX calls from different functions of my code. All these calls have a similar structure with different data/url/callback params:
var jqXHR = $.post('/dba/port.php', {
mode: "del_wallfunds",
pdata: cdata,
wname: wName
},
function (data) {}, "json")
.done(function (data) {
var msg = data.msg;
if (msg.indexOf("Error") == -1) {
alertify.success(msg);
delSelected(selGroup);
} else {
alertify.error(msg);
}
})
.fail(function () {
alertify.error("Error .....");
});
I am thinking how to write a function that would return that var jqXHR to minimize the total size of the code. It is not a problem to pass all static variables like URL, error strings etc. But the problem is that all callback functions on ".done" are different and I don't know how to pass these callback functions as variables.
One way would be to call a single "universal" function on .done and pass a "switch" variable to that function, but it doesn't seem to be an elegant solution.
Any suggestions how to it in some elegant way?
Thanks
Either pass the done callback function as an argument when calling your function:
function ajaxCall(url, data, doneCallback) {
return $.post(url, data, doneCallback, "json").fail(...);
// or
return $.post(url, data, function() {}, "json").done(doneCallback).fail(...);
}
var jqXhr = ajaxCall('yoururl.php', {key: 'value'}, function(data) {
// do something
});
Or return the jqXhr object from the function, and assign the done callback then:
function ajaxCall(url, data) {
return $.post(url, data, function() {}, "json").fail(...);
}
var jqXhr = ajaxCall('yoururl.php', {key: 'value'});
jqXhr.done(function(data) {
// do something
});
Alternatively switch to using jQuery.ajax() instead, and pass the entire options object in:
function ajaxCall(options) {
return $.ajax(options).fail(...);
}
var jqXhr = ajaxCall({
url: 'yoururl.php',
data: {key: 'value'},
dataType: 'json'
});
jqXhr.done(function(data) {
// do something
});
You can try to :
turn "request successfully returned a treatment error" into a "rejected request",
put the "alertify" processing in a common callback
Here is a sketch of what this could give :
function myAjaxApi(url, data){
var myAjaxCall = $.post(url, data, function (data) {}, "json")
.then(function (data) {
// using .then : change "request succesful with error state"
// to "rejected state"
var msg = data.msg;
if (msg !== undefined && msg.indexOf("Error") >= 0) {
var dfd = $.Deferred();
// try to match the same signature as the "error" option
dfd.reject(this, msg);
return dfd;
} else {
return data
}
});
myAjaxCall.done(function(data){
if (data.msg) {
alertify.success(data.msg);
}
}).fail(function (jqxhr, msg) {
if (!msg) { msg = "Error ....."; }
alertify.error(msg);
});
return myAjaxCall;
}
//usage
myAjaxApi('/dba/port.php', {mode: "del_wallfunds", pdata: cdata, wname: wName})
.done(function (data) {
// the ".done()" queue will not be executed if msg contains "Error" ...
delSelected(selGroup);
});
Some parts should be written with more care ; the above example is meant to illustrate how you can wrap your repeated ajax calls inside a common api.
I have the following function:
loadMsgBody: function (id) {
return dojo.xhrGet({
url: "myurl",
handleAs: "text",
content: {
id: id
},
load: function (response) {
return response;
},
error: function (response) {
alert(response);
}
});
}
And calling it:
var text = "";
this.loadMsgBody(this.msgId).then(function (response) {
text = response;
});
Now I expect to get the return value of the function but instead I am getting an empty value for text. However, in Firebug I do see the response from the server with the correct value. I've searched and found these links : DOJO xhrGet how to use returned json object?
and:
Using hitch / deferred with an xhrGet request
But I still can't get and store the data with the above code. I don't want to do the manipulation inside the xhrGet call, I want to retrieve the data and use as it will be used multiple times.
Is there anything I am missing?
Dojo's XHR methods return instances of the class dojo/Deferred, because they are asynchronous. What this means is that the functions returns before the value of the response is available. In order to work with the results of the asynchronous response you need to wait for it to return. Dojo exposes this using a uniform API, Deferreds. Instances of the dojo/Deferred class have a method then. The then method takes a function as a parameter. That function will execute once the Deferred have been resolved (in this case, when the request has completed).
var deferred = loadMsgBody();
deferred.then(function(response){
//work with response
});
I would try changing your load function to evoke your callback function:
loadMsgBody: function (id, callback) {
return dojo.xhrGet({
url: "myurl",
handleAs: "text",
content: {
id: id
},
load: function (response) {
if(callback) {
callback(response);
}
},
error: function (response) {
alert(response);
}
});
}
Try this:
loadMsgBody: function (id, callback) {
return dojo.xhrGet({
url: "myurl",
handleAs: "text",
content: {
id: id
},
load: function (response) {
callback.apply(null,[response]);
},
error: function (response) {
alert(response);
}
});
}
Then:
var text = "";
this.loadMsgBody(this.msgId, function (response) {
text = response;
console.log("text:",text); // this will show your return data
});
console.log("text:",text); // this will show empty data because ajax call is asynchrize, at this time , data not return yet.
setTimeout(function(){
console.log("text:",text); // this will show your return data again because ajax call should have finished after 30000 ms
},30000)
I have a method below:
self.getOrAddCache = function (key, objectFactory) {
var data = self.getFromCache(key);
if (!data) {
data = objectFactory();
if (data && data != null)
self.addToCache(key, data);
}
return data;
};
I use like this:
function getCities()
{
var cities = getOrAddCache(CacheKeys.Cities, function() {
var cityArray = new Array();
// get city informations from service
$.ajax({
type: "GET",
async: true,
url: "service/cities",
success: function (response) {
$.each(response, function(index, value) {
cityArray.push({
name: value.name,
id: value.id
});
});
}
});
if (cityArray.length > 0)
return cityArray;
else {
return null;
}
});
return cities;
}
getCities function always return null because getCities not waiting for completion async ajax request.
How can i resolve this problem? (Request must be async)
The best solution for this is to use Deferred objects. Since you require your AJAX call to be asynchronous, you should have your getCities function return a promise to return that data at some point in the future.
Instead of storing the raw data in the cache, you store those promises.
If you request a promise that has already been resolved, that will complete immediately. If there's already a pending request for the cached object, the async AJAX call will be started and all outstanding callbacks waiting for that promise will be started in sequence.
Something like this should work, although this is of course untested, E&OE, etc, etc.
self.getCached = function(key, objectFactory) {
var def = self.getCache(key);
if (!def) {
def = objectFactory.call(self);
self.addToCache(key, def);
}
return def;
}
function getCities() {
return getCached(CacheKeys.Cities, function() {
return $.ajax({
type: 'GET',
url: 'service/cities'
}).pipe(function(response) {
return $.map(response, function(value) {
return { name: value.name, id: value.id };
});
});
});
}
Note the usage of .pipe to post-process the AJAX response into the required format, with the result being another deferred object, where it's actually the latter one that gets stored in your cache.
The usage would now be:
getCities().done(function(cities) {
// use the cities array
});
With a callback:
function getCities(callbackFunction)
{
var cities = getOrAddCache(CacheKeys.Cities, function() {
var cityArray = new Array();
// get city informations from service
$.ajax({
type: "GET",
async: true,
url: "service/cities",
success: function (response) {
$.each(response, function(index, value) {
cityArray.push({
name: value.name,
id: value.id
});
});
callbackFunction(cityArray);
}
});
});
}
getCities(function(cityArray){
// do stuff
});
You can't return the result from a function fetching asynchronously the data.
Change your getCities function to one accepting a callback :
function fetchCities(callback) {
var cities = getOrAddCache(CacheKeys.Cities, function() {
var cityArray = new Array();
// get city informations from service
$.ajax({
type: "GET",
async: true,
url: "service/cities",
success: function (response) {
$.each(response, function(index, value) {
cityArray.push({
name: value.name,
id: value.id
});
});
if (callback) callback(cityArray);
}
});
});
}
And use it like this :
fetchCities(function(cities) {
// use the cities array
});
Note that it's technically possible, using async:true, to make the code wait for the response but don't use it : that's terrible practice and it locks the page until the server answers.
You seem to be contradicting yourself.
Something that is asynchronous, by definition, does not pause the script to wait for the end of it's execution. If it does wait, it cannot be asynchronous.
The best wayto fix this is by adding a callback function in your ajax success function that passes the end result to another function, which handles the rest of the execution.
I'm trying to create a global handler that gets called before the ajax success callback. I do a lot of ajax calls with my app, and if it is an error I return a specific structure, so I need to something to run before success runs to check the response data to see if it contains an error code bit like 1/0
Sample response
{"code": "0", "message": "your code is broken"}
or
{"code": "1", "data": "return some data"}
I can't find a way to do this in jQuery out of the box, looked at prefilters, ajaxSetup and other available methods, but they don't quite pull it off, the bets I could come up with is hacking the ajax method itself a little bit:
var oFn = $.ajax;
$.ajax = function(options, a, b, c)
{
if(options.success)
{
var oFn2 = options.success;
options.success = function(response)
{
//check the response code and do some processing
ajaxPostProcess(response);
//if no error run the success function otherwise don't bother
if(response.code > 0) oFn2(response);
}
}
oFn(options, a, b, c);
};
I've been using this for a while and it works fine, but was wondering if there is a better way to do it, or something I missed in the jQuery docs.
You can build your own AJAX handler instead of using the default ajax:
var ns = {};
ns.ajax = function(options,callback){
var defaults = { //set the defaults
success: function(data){ //hijack the success handler
if(check(data)){ //checks
callback(data); //if pass, call the callback
}
}
};
$.extend(options,defaults); //merge passed options to defaults
return $.ajax(options); //send request
}
so your call, instead of $.ajax, you now use;
ns.ajax({options},function(data){
//do whatever you want with the success data
});
This solution transparently adds a custom success handler to every $.ajax() call using the duck punching technique
(function() {
var _oldAjax = $.ajax;
$.ajax = function(options) {
$.extend(options, {
success: function() {
// do your stuff
}
});
return _oldAjax(options);
};
})();
Here's a couple suggestions:
var MADE_UP_JSON_RESPONSE = {
code: 1,
message: 'my company still uses IE6'
};
function ajaxHandler(resp) {
if (resp.code == 0) ajaxSuccess(resp);
if (resp.code == 1) ajaxFail(resp);
}
function ajaxSuccess(data) {
console.log(data);
}
function ajaxFail(data) {
alert('fml...' + data.message);
}
$(function() {
//
// setup with ajaxSuccess() and call ajax as usual
//
$(document).ajaxSuccess(function() {
ajaxHandler(MADE_UP_JSON_RESPONSE);
});
$.post('/echo/json/');
// ----------------------------------------------------
// or
// ----------------------------------------------------
//
// declare the handler right in your ajax call
//
$.post('/echo/json/', function() {
ajaxHandler(MADE_UP_JSON_RESPONSE);
});
});
Working: http://jsfiddle.net/pF5cb/3/
Here is the most basic example:
$.ajaxSetup({
success: function(data){
//default code here
}
});
Feel free to look up the documentation on $.ajaxSetup()
this is your call to ajax method
function getData(newUrl, newData, callBack) {
$.ajax({
type: 'POST',
contentType: "application/json; charset=utf-8",
url: newUrl,
data: newData,
dataType: "json",
ajaxSuccess: function () { alert('ajaxSuccess'); },
success: function (response) {
callBack(true, response);
if (callBack == null || callBack == undefined) {
callBack(false, null);
}
},
error: function () {
callBack(false, null);
}
});
}
and after that callback success or method success
$(document).ajaxStart(function () {
alert('ajax ajaxStart called');
});
$(document).ajaxSuccess(function () {
alert('ajax gvPerson ajaxSuccess called');
});