Is it possible to perform an action before every http request sent upon clicking an a-href tag? I would like to perform the action before every referred http request as well (eg requests for images/scripts in the DOM). Thanks!
It can be achieved for every HTTP ajax request.
Note : Dummy requests in examples are made to HTTP Bin.
JAVASCRIPT:
References : JS XMLHttpRequest
(function init()
{
XMLHttpRequest.prototype._open = XMLHttpRequest.prototype.open;
XMLHttpRequest.prototype.open = function(method, url, async, user, password){
initialChanges();
this._open(method, url, async, user, password);
};
})();
function initialChanges()
{
alert("Making a Javascript ajax request.");
}
function makeRequestViaXHR()
{
var req = new XMLHttpRequest();
req.open("GET","https://httpbin.org/get",false,null,null);
req.onreadystatechange=function(){
if(req.readyState === 4)
{
if(req.status === 200)
{
console.log(req.responseText);
}
else
{
console.log("Request Failed");
}
}
};
req.send();
}
<button onclick="makeRequestViaXHR()">Make a dummy ajax request via Javascript</button>
JQUERY:
References : jQuery ajax, jQuery .ajaxSend
(function init()
{
$(document).ajaxSend(function(event,xhr,settings){
alert("Making a jQuery ajax request.");
});
})();
function makeRequestViaJquery()
{
$.ajax({
url:"https://httpbin.org/get",
method:"GET",
async:true,
success:function(response){
console.log(response);
},
error:function(error){
console.log(error);
}
});
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button onclick="makeRequestViaJquery()">Make a dummy ajax request via jQuery</button>
In case of navigating to other pages, downloading files or mail addresses via <a> tag, execute the method on click using addEventListener.
References : HTML Element Subinterfaces
document.addEventListener("click", function(event){
var elem = event.target;
if(elem instanceof HTMLAnchorElement) //For <a> tag
{
executeThis();
}
});
function executeThis()
{
alert("Element is clicked");
}
Click this anchor element
Download Image
Scripts execute only after the DOM is loaded. If some function need to be executed before loading the images, you need to add the method with a script tag before every img element. Refer this for more info.
Currently, I am trying to show a spinner while making an HTTP request that will end when the call completes. I have built several different spinners but all stop animation the second the call begins.
var spinnerArray = [];
for (var i = 0; i < 20; i++) {
spinnerArray.push('/images/preloaderGif/preloader'+ ("0" + i).slice(-2) + '.gif');
}
$.spinner.images = spinnerArray;
$.spinner.duration = "200";
$.spinner.repeatCount = "0";
spin();
function spin(){
$.spinner.start();
callHTTP() //Prewritten function
Ti.App.addEventListener('callEnd', function(e){
$.spinner.stop();
});
}
This results in the spinner never appearing. Taking the call out or nesting it within a timeout causes the spinner to spin infinitely, or until the timeout ends.
Is there a way to have the spinner continue to spin through the call?
Actually, there's a far better & super easy way to show an indicator. Just follow below steps.
Download this widget Loading Indicator Widget & add it to your project in app->widgets folder. Create widget folder if it doesn't exist.
Add this line "nl.fokkezb.loading" : "*" into your app->config.json file within dependencies dictionary as shown in below screenshot.
Add this line Alloy.Globals.loading = Alloy.createWidget("nl.fokkezb.loading"); in your alloy.js file
Finally, you can use this code to show/hide indicator properly while calling HTTP requests.
function callHTTP() {
if (!Ti.Network.online) {
return;
}
Alloy.Globals.loading.show();
var xhr = Ti.Network.createHTTPClient({
onerror : function(e) {
Alloy.Globals.loading.hide();
},
onload : function(e) {
Alloy.Globals.loading.hide();
// run your additional code here
},
});
xhr.open("GET", url);
xhr.send();
}
callHTTP();
Using this widget, you won't need to write long, error-prone codes for different projects. Just add this widget & you can show/hide loading indicator with just 2 lines of code.
Remember one thing that XHR error/success callbacks are the only places where you can write code to hide the indicators as you can never be sure when the HTTP request will complete.
You could use an ActivityIndicator : http://docs.appcelerator.com/platform/latest/#!/api/Titanium.UI.ActivityIndicator
$.activityIndicator.show();
var xhr = Ti.Network.createHTTPClient({
onerror : function(e) {
// code
$.activityIndicator.hide();
},
onload : function(e) {
// code
$.activityIndicator.hide();
},
});
xhr.open("GET", url);
xhr.send();
Is it possible that using jQuery, I cancel/abort an Ajax request that I have not yet received the response from?
Most of the jQuery Ajax methods return an XMLHttpRequest (or the equivalent) object, so you can just use abort().
See the documentation:
abort Method (MSDN). Cancels the current HTTP request.
abort() (MDN). If the request has been sent already, this method will abort the request.
var xhr = $.ajax({
type: "POST",
url: "some.php",
data: "name=John&location=Boston",
success: function(msg){
alert( "Data Saved: " + msg );
}
});
//kill the request
xhr.abort()
UPDATE:
As of jQuery 1.5 the returned object is a wrapper for the native XMLHttpRequest object called jqXHR. This object appears to expose all of the native properties and methods so the above example still works. See The jqXHR Object (jQuery API documentation).
UPDATE 2:
As of jQuery 3, the ajax method now returns a promise with extra methods (like abort), so the above code still works, though the object being returned is not an xhr any more. See the 3.0 blog here.
UPDATE 3: xhr.abort() still works on jQuery 3.x. Don't assume the update 2 is correct. More info on jQuery Github repository.
You can't recall the request but you can set a timeout value after which the response will be ignored. See this page for jquery AJAX options. I believe that your error callback will be called if the timeout period is exceeded. There is already a default timeout on every AJAX request.
You can also use the abort() method on the request object but, while it will cause the client to stop listening for the event, it may probably will not stop the server from processing it.
Save the calls you make in an array, then call xhr.abort() on each.
HUGE CAVEAT: You can abort a request, but that's only the client side. The server side could still be processing the request. If you are using something like PHP or ASP with session data, the session data is locked until the ajax has finished. So, to allow the user to continue browsing the website, you have to call session_write_close(). This saves the session and unlocks it so that other pages waiting to continue will proceed. Without this, several pages can be waiting for the lock to be removed.
It's an asynchronous request, meaning once it's sent it's out there.
In case your server is starting a very expensive operation due to the AJAX request, the best you can do is open your server to listen for cancel requests, and send a separate AJAX request notifying the server to stop whatever it's doing.
Otherwise, simply ignore the AJAX response.
AJAX requests may not complete in the order they were started. Instead of aborting, you can choose to ignore all AJAX responses except for the most recent one:
Create a counter
Increment the counter when you initiate AJAX request
Use the current value of counter to "stamp" the request
In the success callback compare the stamp with the counter to check if it was the most recent request
Rough outline of code:
var xhrCount = 0;
function sendXHR() {
// sequence number for the current invocation of function
var seqNumber = ++xhrCount;
$.post("/echo/json/", { delay: Math.floor(Math.random() * 5) }, function() {
// this works because of the way closures work
if (seqNumber === xhrCount) {
console.log("Process the response");
} else {
console.log("Ignore the response");
}
});
}
sendXHR();
sendXHR();
sendXHR();
// AJAX requests complete in any order but only the last
// one will trigger "Process the response" message
Demo on jsFiddle
We just had to work around this problem and tested three different approaches.
does cancel the request as suggested by #meouw
execute all request but only processes the result of the last submit
prevents new requests as long as another one is still pending
var Ajax1 = {
call: function() {
if (typeof this.xhr !== 'undefined')
this.xhr.abort();
this.xhr = $.ajax({
url: 'your/long/running/request/path',
type: 'GET',
success: function(data) {
//process response
}
});
}
};
var Ajax2 = {
counter: 0,
call: function() {
var self = this,
seq = ++this.counter;
$.ajax({
url: 'your/long/running/request/path',
type: 'GET',
success: function(data) {
if (seq === self.counter) {
//process response
}
}
});
}
};
var Ajax3 = {
active: false,
call: function() {
if (this.active === false) {
this.active = true;
var self = this;
$.ajax({
url: 'your/long/running/request/path',
type: 'GET',
success: function(data) {
//process response
},
complete: function() {
self.active = false;
}
});
}
}
};
$(function() {
$('#button').click(function(e) {
Ajax3.call();
});
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input id="button" type="button" value="click" />
In our case we decided to use approach #3 as it produces less load for the server. But I am not 100% sure if jQuery guarantees the call of the .complete()-method, this could produce a deadlock situation. In our tests we could not reproduce such a situation.
It is always best practice to do something like this.
var $request;
if ($request != null){
$request.abort();
$request = null;
}
$request = $.ajax({
type : "POST", //TODO: Must be changed to POST
url : "yourfile.php",
data : "data"
}).done(function(msg) {
alert(msg);
});
But it is much better if you check an if statement to check whether the ajax request is null or not.
Just call xhr.abort() whether it's jquery ajax object or native XMLHTTPRequest object.
example:
//jQuery ajax
$(document).ready(function(){
var xhr = $.get('/server');
setTimeout(function(){xhr.abort();}, 2000);
});
//native XMLHTTPRequest
var xhr = new XMLHttpRequest();
xhr.open('GET','/server',true);
xhr.send();
setTimeout(function(){xhr.abort();}, 2000);
You can abort any continuous ajax call by using this
<input id="searchbox" name="searchbox" type="text" />
<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
<script type="text/javascript">
var request = null;
$('#searchbox').keyup(function () {
var id = $(this).val();
request = $.ajax({
type: "POST", //TODO: Must be changed to POST
url: "index.php",
data: {'id':id},
success: function () {
},
beforeSend: function () {
if (request !== null) {
request.abort();
}
}
});
});
</script>
As many people on the thread have noted, just because the request is aborted on the client-side, the server will still process the request. This creates unnecessary load on the server because it's doing work that we've quit listening to on the front-end.
The problem I was trying to solve (that others may run in to as well) is that when the user entered information in an input field, I wanted to fire off a request for a Google Instant type of feel.
To avoid firing unnecessary requests and to maintain the snappiness of the front-end, I did the following:
var xhrQueue = [];
var xhrCount = 0;
$('#search_q').keyup(function(){
xhrQueue.push(xhrCount);
setTimeout(function(){
xhrCount = ++xhrCount;
if (xhrCount === xhrQueue.length) {
// Fire Your XHR //
}
}, 150);
});
This will essentially send one request every 150ms (a variable that you can customize for your own needs). If you're having trouble understanding what exactly is happening here, log xhrCount and xhrQueue to the console just before the if block.
I was doing a live search solution and needed to cancel pending requests that may have taken longer than the latest/most current request.
In my case I used something like this:
//On document ready
var ajax_inprocess = false;
$(document).ajaxStart(function() {
ajax_inprocess = true;
});
$(document).ajaxStop(function() {
ajax_inprocess = false;
});
//Snippet from live search function
if (ajax_inprocess == true)
{
request.abort();
}
//Call for new request
Just use ajax.abort() for example you could abort any pending ajax request before sending another one like this
//check for existing ajax request
if(ajax){
ajax.abort();
}
//then you make another ajax request
$.ajax(
//your code here
);
there is no reliable way to do it, and I would not even try it, once the request is on the go; the only way to react reasonably is to ignore the response.
in most cases, it may happen in situations like: a user clicks too often on a button triggering many consecutive XHR, here you have many options, either block the button till XHR is returned, or dont even trigger new XHR while another is running hinting the user to lean back - or discard any pending XHR response but the recent.
The following code shows initiating as well as aborting an Ajax request:
function libAjax(){
var req;
function start(){
req = $.ajax({
url: '1.php',
success: function(data){
console.log(data)
}
});
}
function stop(){
req.abort();
}
return {start:start,stop:stop}
}
var obj = libAjax();
$(".go").click(function(){
obj.start();
})
$(".stop").click(function(){
obj.stop();
})
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="button" class="go" value="GO!" >
<input type="button" class="stop" value="STOP!" >
If xhr.abort(); causes page reload,
Then you can set onreadystatechange before abort to prevent:
// ↓ prevent page reload by abort()
xhr.onreadystatechange = null;
// ↓ may cause page reload
xhr.abort();
I had the problem of polling and once the page was closed the poll continued so in my cause a user would miss an update as a mysql value was being set for the next 50 seconds after page closing, even though I killed the ajax request, I figured away around, using $_SESSION to set a var won't update in the poll its self until its ended and a new one has started, so what I did was set a value in my database as 0 = offpage , while I'm polling I query that row and return false; when it's 0 as querying in polling will get you current values obviously...
I hope this helped
I have shared a demo that demonstrates how to cancel an AJAX request-- if data is not returned from the server within a predefined wait time.
HTML :
<div id="info"></div>
JS CODE:
var isDataReceived= false, waitTime= 1000;
$(function() {
// Ajax request sent.
var xhr= $.ajax({
url: 'http://api.joind.in/v2.1/talks/10889',
data: {
format: 'json'
},
dataType: 'jsonp',
success: function(data) {
isDataReceived= true;
$('#info').text(data.talks[0].talk_title);
},
type: 'GET'
});
// Cancel ajax request if data is not loaded within 1sec.
setTimeout(function(){
if(!isDataReceived)
xhr.abort();
},waitTime);
});
This is my implementation based on many answers above:
var activeRequest = false; //global var
var filters = {...};
apply_filters(filters);
//function triggering the ajax request
function apply_filters(filters){
//prepare data and other functionalities
var data = {};
//limit the ajax calls
if (activeRequest === false){
activeRequest = true;
}else{
//abort if another ajax call is pending
$request.abort();
//just to be sure the ajax didn't complete before and activeRequest it's already false
activeRequest = true;
}
$request = $.ajax({
url : window.location.origin + '/your-url.php',
data: data,
type:'POST',
beforeSend: function(){
$('#ajax-loader-custom').show();
$('#blur-on-loading').addClass('blur');
},
success:function(data_filters){
data_filters = $.parseJSON(data_filters);
if( data_filters.posts ) {
$(document).find('#multiple-products ul.products li:last-child').after(data_filters.posts).fadeIn();
}
else{
return;
}
$('#ajax-loader-custom').fadeOut();
},
complete: function() {
activeRequest = false;
}
});
}
I have this function
function Overlap() {
setTimeout(function() {
$(".overlap").each(function(index, object) {
var image = $(this).prev().attr('src');
target = $(object);
var xmlhttp
xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function() {
if(xmlhttp.status == 200 && xmlhttp.readyState == 4) {
xresponse = xmlhttp.responseText.split('-');
$(target).children('a').attr('href', xresponse[0]);
$(target).children('.name').html(xresponse[1]); //Set returned array appropriately
$(target).children('.age').html(xresponse[2]);
$(target).children('.specialization').html(xresponse[3]);
}
}
xmlhttp.open('POST', 'factory/operational.php', true);
xmlhttp.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
xmlhttp.send('overlap=overlap&image=' + image);
});
}, 1000);
}
Html:
<div class="Divbox" id="Box_three"><img src='<?php ?>' />
<div class="overlap">
<a href='' class='name'></a>
<div class='age'></div>
<div class='specialization'></div>
</div>
</div>
And it is called by this
window.onload = Overlap();
From the page that uses it
The problem is the function works .. it is usually called properly and i put the
window.onload & setTimeout functionality to make sure that the page loads fully before trying to grab the .overlap element.
Now what is wrong is when overlap is called there are about 48 of the .overlap div element on the page and they all send this request to the operational.php page but, on arrival back they do not appropriate properly, they only appropriate on the last element that comes back from operational.php, can someone help me find the right selector instance to pass to make sure that each instance of the overlap and is children receives the response accordlingly
you missed declaring your target variable, making it global.
target = $(object);
should be
var target = $(object);
without var, every iteration of the loop will use the same target, meaning all xhr request complete callbacks will use the same target.
Example:
$.each(["a","b","c"], function(i,val) {
x = val;
console.log(x); // "a", "b", "c"
});
console.log(x); //"c"
After the each is complete, x will be a global var that contains the value from the last iteration. In your code, you're performing an asynchronous action on each iteration, meaning, the callbacks for each action will happen after the each is complete, which is why target points to the last iteration for all of the callbacks.