I am kind of confused right now. I have the following asynchronous ajax call where I am passing a successcallback.
ajax('PUT', 'some URL', successCallback, data);
I observe that this callback is called when the request completes so I fail to understand how this call is asynchronous if it waits for the call to complete.
If I do not pass the successcallback to ajax and return the callback from the function I can observe asynchronous behavior as expected
ajax('PUT', 'some URL', undefined, data);
return successcallback();
With above change I actually observe the ajax call executing asynchronously and my page can proceed but if the page redirects to some other link the the request gets cancelled. So the only option that works is passing in succesCallback for ajax but it seems to be syncronous rather than asynchronous
I think you have your terminology backwards. "Asynchronous" in this context means "runs at some future point in time and doesn't block immediate execution of code". "Synchronous" is a blocking call, one that will halt execution until it's complete.
The callback there is intended to be executed when the request is complete, which is by definition "asynchronous". Your alternate version runs the success callback regardless, and it does that long before the AJAX call is initiated as well as not knowing if it will succeed.
You need to do asynchronous calls otherwise the JavaScript code and engine are completely jammed waiting for a response. This used to be acceptable when this is a separate process with no other responsibilities, but it's a disaster in a web application where your code likely has other things it has to respond to.
Related
I have an axios call that I cancel, this is then caught using catch to display a message.
After this, I have chained a then(), but then() is called even if I cancel the request.
How can I make it so that then() is called only if the request is not cancelled?
Your question is hard to answer without much context. But if I understand you correctly I think what you are looking for is to delay the axios request and wait a few seconds to ensure it hasn't been cancelled before sending the request. This is called a concurrency method. Using setTimeout() will wait a certain amount of time before running any code inside of it. It is also very good to ensure users do not spam requests to your end point and wait for the newest and most recent request and return that back (if you decide to wrap your whole request in a timeout):
return axios.get('your-end-point').then(response => setTimeout(response, 1000)));
Note: 1000 here is 1000 m/s. You can change this value to be longer or shorter depending on how long you wish to wait for.
See more about setTimeout and concurrency here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/EventLoop
I know this question has been asked multiple times before as how to execute function when all AJAX call has been completed. We can user jquery.stop() in this case.
But my requirement is different. I want to show confirm banner when all ajax call have been executed successfully. For different pages , I have multiple AJAX calls. I do not want to put any condition on each AJAX call success method.
Can any one suggest if there is any global way.
Thanks in advance.
your are searching for global event handlers:
https://api.jquery.com/category/ajax/global-ajax-event-handlers/
http://api.jquery.com/ajaxcomplete/
anytime when you call an ajax request you "see" it via .ajaxSend() and handle response via .ajaxComplete()
In my webpage many on-load ajax call those works fine.
Action takes time as per processing time. Means if any action that has been complete will send response and will not wait for first to finish.
But if same I am trying to do with on-lick or any user event. All ajax call works synchronously. I want these should not wait to finish the execution of first running action. All should start and complete independently.
I am using jquery 1.8 where default async= true;
Please help me here to resolve this.
Issue may be due to session lock.
more detail you can find it here
http://php.net/manual/en/function.session-write-close.php
call session_write_close function if there no session write activity in your script or function.
Such issues are observed in many concurrent ajax call and previous call has some session write activity. In this case session will be locked until it completed its execution.
If you set async to true, they will all fire at the same time.
make explicitly declaration of async = true option in each ajax call .
Useful jsfiddle link
http://jsfiddle.net/jquerybyexample/tS349/
hi I want to ask about AJAX ,either AJAX makes Synchronous or Asynchronous calls to the Server.As from its name It is ASYNCHRONOUS JS & XML ,but when it comes to sending request to server,it is synchronous or Asynchronous?Help will be Appreciated
It's a loosely defined buzzword. JS can make both. Synchronous calls are locking and should almost always be avoided though.
I think it would help you if you had a definition of what synchronous and asynchronous mean in this context.
A synchronous call blocks the execution of the Javascript thread that executed it. This means if you have the following code:
console.log('Before');
xhr.send();
console.log('After');
You will not see the After message until the request has completed and the server has returned data.
An asynchronous call does not block the execution of the Javascript thread that executed it. This means that, for the same code block above, the After message fires immediately, and does not wait for the request to finish. Because the execution of the code continues in an asynchronous call, you need to use a callback to handle the result. This is what the onreadystatechange() event/method is for.
You can choose which type of call is made, synchronous or asynchronous, when you call the open() method of the XmlHttpRequest object. By passing true to the third argument, the request is asynchronous, if you pass false it is synchronous.
It can actually be both, sync and async.
indeed, it can be both synchronuous and asynchronuous. When the call is made synchronuously, your code doesn't continue until the request has been completed and a response has been received. This is not what you want in many cases, since this freezes all javascript driven parts of your website.
The Request is asynchronous because the Browser must not wait for the response of the request. So that means on the one hand you can have a synchronous for example you send your request and show a wait-screen but on the other hand you can send your request to the server and the server responds at any time. Your browser can process the response but the user can work without any influences with you page.
If I have a JS function as follows;
function testFn()
{
x.ajaxMethod(param1,JScallBackFunction); //Please do not worry about the syntax..this just indicates an external method call
alert("Line after ajaxMethod");
}
The ajaxMethod(), lets say is some kind of method defined in an external Java file (so it can be through DWR or anything) which returns some data...Point is it takes some time to execute this line of code...
Now my question is when will the alert on next line get fired (i.e. alert("Line after ajaxMethod");)
Will it wait for these 2 things to complete (ajaxMethod execution as well as JScallBackFunction)
OR
It will be fired immediately without waiting for any of the above 2 things to complete ?
Also if you could guide in general about the JavaScript method flow execution, that will be great.
It depends. Ajax calls are usually asynchronous which means the execution of code will not be paused until the asynchronous function returns. Therefore the alert will be executed immediately.
Asynchronous functions in javascript are usually to do with Ajax and loading something from a remote server. If you do wish to force JavaScript to wait while loading that content then you can set a flag for the XMLHTTPRequest object.
this is a good question to read: When is JavaScript synchronous?
it will fire immediately after the ajax call. if you want it to wait put it in the callback function.
edit: a method that defines a callback is essentially this:
function(param1, callback) {
// do stuff
callback(); // execute callback
}
First, when you say
The ajaxMethod(), lets say is some
kind of method defined in an external
Java file
I suppose you really mean external JavaScript file.
When you send an Ajax request, you ask the browser to send a request to the server for you.
This request on the server may take sometime and you don't want to "wait" on it. (This is the whole idea of Async requests - stuff in the background).
So you tell the browser, here send this request to the server. Don't bother me unless the server responds, and once the server responds (we have a "response"), call this method. This is called callback. The method is called at a later point, when the response comes.
So the statement
x.ajaxMethod(param1,JScallBackFunction);
(assuming that it does gets a XmlHttpRequest, initializes it and calls the send method on it*) actually does two things:
Sends the Ajax request
Registers a call back function that will be called when the server responds (when we have an response). JScallBackFunction will be called when there is an response from the server.
But since this is an asynchronous request, the browser does not "wait" instead it continues to the next statement (if there is one) after the Ajax call and executes it.
So, alert("Line after ajaxMethod"); will be executed immediately.
*If this does not make any sense for you, this is how an Ajax request is actually "created" and "sent". This article may help you understand.