Ajax and session variable - javascript

Imagine this scenario:
I have a link that fires up a JavaScript function(has an Ajax request in it).
The JavaScript function has a parameter passed by the link's onclick='jsFunction(param)'.
The JavaScript function sends the parameter value in a function inside a controller that sets the param value to a session variable.
The function in the controller will then send the new value of the session variable back to the JavaScript function's Ajax request.
When the data reached into the Ajax request, another function will be called using the data being passed.
Question:
Since I am talking about the session variable's value being passed to an Ajax request, how can I process the data came from the link to the second function in real-time? I want to post the code here but it's too verbose with the info I only need.
The current state of my code is that, I can't fetch the right/latest data. Instead, I get the previous data came from the previous link I clicked.
Is there an Ajax feature that I can only proceed to the next function if the first function is done processing the latest data?
Any help will be much appreciated.

You can use the callback to any of the jQuery AJAX methods to delay execution of another function until after the request is complete.
$.post('/some/url', somedata, function(returnData) {
// put the code you want to execute on completion here
});
or If you have already defined your function to be called after returning data, you can just write like this:
$.post('/some/url', somedata, processData);

Related

How does it make sense to use the variable name used to name a function inside that same function?

In this snippet, from the Angular documentation on $resource, the name of the function is user and inside the function they are using a variable of the same name.
var User = $resource('/user/:userId', {userId:'#id'});
var user = User.get({userId:123}, function() {
user.abc = true;
user.$save();
});
How does that make sense? And what are the rules around this?
When you call User.get(), it returns a promise, and processing continues. When that promise resolves, angular sets the variable you set it to, in this case user, to the value of the resolution. It also calls the success callback function, so you can safely change it at that point.
To use the above example, here is what happens.
you call `User.get({userId:123})
User.get returns a promise and sets var user to that promise
processing continues
the promise resolves, let's say to {id:123,name:"Imray"}
angular sets the variable user to {id:123,name:"Imray"}
angular calls your success callback, in which you:
set user.abc to true, so your object now is {id:123,name:"Imray",abc:true}
you call user.$save(), which saves it to the server, etc.
Essentially, there is nothing wrong with it, just be aware of the order of execution.
"user" is not name of function, its name of object which is read from given resource.
To be correct. User become proxy which is filled with data when http request is done.
Second parameter - function is callback which is called after user is successfully loaded, so user become fully created object.
So when .get is called it works exactly like that:
create variable user with "proxy"
read user from /user/123
actualize user varible with data and "resource's methods" ($save, $delete...)
call given function callback in which:
set abc in user object
save it back to the resource ($save introduces POST to /user/123
In documentation you can read: https://docs.angularjs.org/api/ngResource/service/$resource -
(part Usage/Returns)
"It is important to realize that invoking a $resource object method
immediately returns an empty reference (object or array depending on
isArray). Once the data is returned from the server the existing
reference is populated with the actual data. This is a useful trick
since usually the resource is assigned to a model which is then
rendered by the view. Having an empty object results in no rendering,
once the data arrives from the server then the object is populated
with the data and the view automatically re-renders itself showing the
new data. This means that in most cases one never has to write a
callback function for the action methods."
"user" doesnt have to be passed as parameter because user is set before callback is called.

Issue with multiple ajax calls simultaneously using jquery

I am using jquery for ajax calls
All the calls are called immmediately on page load and we are getting the responses at almost the same time.
the issue is, the 3 calls are fired and I am getting the data, but the callback function is fired for the first call only.
the other two callbacks are not called, the callback is defined as a separate function,
If I just write an alert instead of calling the callback method, all the 3 alert message are coming
So the issue is when we write the callback method, do any one have any idea of the strange behaviour?
We tried to reorder the calls, the behaviour is similar, which ever is called first, its callback will be called, for the rest, it will not be called
var url = "/test1";
ajaxCall(url, testMethod1, false);
var url = "test2";
ajaxCall(url, testMethod2, false);
var url = "test3";
ajaxCall(url, testMethod3, false);
testMethod1:function(data){
console.log("first"+data);
},
testMethod2:function(data){
console.log("second"+data);
},
testMethod3:function(data){
console.log("thrid"+data);
}
ajaxCall is defined as jquery ajax, the issue is only the testMethod1 is called, the rest 2 are not called
Regards
Hari
Well the thing that immediately caught my eye is that the URL for test1 has a forward slash preceding test1. This means that you are using a valid link in only test1. The alerts will trigger because you are probably not trying to access the data returned (which would still work even though the ajax request fails), where as you are trying to access the data in the coded call back functions you have provided, which will obviously throw a NullPointerException or whatever the equivalent as the ajax call fails due to an incorrect URL. Therefore data never gets set and the code doesn't work.

$.ajax() callbacks are not bound to their specific request?

The code is very complex so i have simplified below in order to confirm if the behavior i am experiencing is normal or due so some other error i have made in the code.
I have two separate ajax requests that each have their own unique call back. I do not care which one completes first and one has no dependency on the other
function ajax(url, cbS){
$.ajax({
url: url,
contentType: 'application/json',
dataType: 'json',
success: function(data){
cbS(data)
},
});
}
function callbackSuccess1(data){
$('#div1').html(data)
}
function callbackSuccess2(data){
$('#div2').html(data)
}
//request#1
ajax(myapiurl+'&peram1=100', callbackSuccess1);
//request#2
ajax(myapiurl+'&peram2=200', callbackSuccess2);
The problem: Sometimes callbackSuccess1 gets the data intended for request#2 and vice versa.
It seems that which ever request completes first fires callbackSuccess1 and the second to complete fires callbackSuccess2.
I need the callback to be bound to it's specific request so that regardless of the order in which they complete each request fires it's proper callback.
OTHER INFO: My backed is django-tastypie, at this point i am thinking that tastypie is somehow messing up the response. That is the only logical conclusion, given that the javascript seems to be immutable.
The proof that this is actually occurring is that when i inspect the responce on request#1 the data objects are clearly intended for request#2...
CONCLUSION:
Thanks for confirming that 'each invocation of your ajax() function will create it's own closure'. This was what i thought was going wrong. I found the problem in my API. I was doing some funky stuff and it looks like I had a variable that was not getting trashed in time causing the API to return the wrong data if the first request took longer than the second.
The only issue I see with the code you have included is that the function argument is cbS, but you are calling cbs(data) - note the different capitalization.
Other than that, each invocation of your ajax() function will create it's own closure and have it's own arguments and those arguments will be preserved separately for the internal success callback. This is an important capability in javascript and it works. It does not get the arguments of one call confused with the callback of another as long as you are not using any global variables or state that might change during the execution of the asynchronous ajax call.
You could probably use jsonp and specify callback query parameter in URL for $.ajax
callback would be the name of javascript function which is to be invoked whenever the response is returned from server.
For more details please refer jquery doc : http://api.jquery.com/jQuery.ajax/
For theory : http://en.wikipedia.org/wiki/JSONP
This is mainly used for cross-site ajax calls.

Execute a method whenever some method has finished executing completely

I've a javascript method defined as follows:
updtCrtEdtPage = function() {PrimeFaces.ab({source:'j_id_ev',formId:'j_id_es',process:'typeNewLOB_in lobIdForEdit j_id_ev',update:'createLOBFullPagePanel',oncomplete:function(xhr,status,args){prepareForCrtEdtFullPage();},params:arguments[0]});}
I want to execute certain method (afterComplete()) whenever this method has finished executing. (This method actually initiates an ajax request & appends the received HTML data on the DOM). So I want my afterComplete() method to be executed whenever ajax response has been received.
I cannot directly do like:
updtCrtEdtPage();
afterComplete();
as this would call the afterComplete() soon after ajax request is initiated & not completely finished executing yet.
Is there any JS/ jQuery way I could do that ?
You could pass afterComplete as a parameter so your function can call it when the ajax call is complete. Something like this...
updtCrtEdtPage = function(callback) {
PrimeFaces.ab({
source:'j_id_ev',
formId:'j_id_es',
process:'typeNewLOB_in lobIdForEdit j_id_ev',
update:'createLOBFullPagePanel',
oncomplete:function(xhr,status,args){
prepareForCrtEdtFullPage();
callback();
},
params:arguments[0]
});
}
updtCrtEdtPage(afterComplete);
Since you say you can't modify updtCrtEdtPage, but you can modify prepareForCrtEdtFullPage I'd suggest using a global variable to determine which callback function to call when the method is complete...
updtCrtEdtPageCallback = afterComplete;
and then in prepareForCrtEdtFullPage just add the last line...
updtCrtEdtPageCallback();
The first method is tidier, but the second will suffice for your particular situation.
your updtCrtEdtPage = function() has an oncomplete callback which is called when the ajax response has been received, add your afterComplete function in that callback and it will execute after the ajax request has been completed.
oncomplete:function(xhr,status,args){
prepareForCrtEdtFullPage();
afterComplete()
}

Need to wait until XMLHttpRequest completes

Whenever I try to find answer of this question everyone refers to ajax start/stop etc.
I am using XUI JS's XHR function for cross domain calling, now I want exactly like this
callMyXHRfunction();
callNextFunctionWhenAboveFunctionResponded();
i.e. I should move forward until unless my xhr function responds (either success or failure)
Update
Use Case:
There is a function called getAllData(), this function get all my current data submitted to server. I need to call this function often to get the latest data and move ahead. While loggin I call this function to get latest data and after every 10 mins I need to call this to get data refreshed.
So if I call each my function on success function then my code may confuse other developer and if I write like above he/she will easily know what is going on in first line and in 2nd line.
Hope now everyone understand my situation very well.
See third example on the website you are referencing:
x$( selector ).xhr( url, fn );
Second argument can be a callback, callback being the keyword you were probably looking for to begin with.
Alternatively, use a synchronous call by supplying async: false as an option.
x$("body").xhr("http://the-url",{ async: false });
Control flow will pause until the request returned and only then continue with your next function. See http://jsfiddle.net/ZQ9uw/ for reference.
You need to make the .xhr call in a way that specifies a callback function and pass in your "next" function as the callback.
So you'd write it like this:
callMyXHRFunction(nextFunctionToCall); // no parens after nextFunctionToCall!
function callMyXHRFunction(callback) {
$("something").xhr(url, {
error: callback, // so that nextFunctionToCall is called on error
callback: callback, // so that nextFunctionToCall is called on success
async: true
// add more options here
});
}

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