Note: simplified example..
I've got a page with 1000 table rows. For each row, i need to "do some work" on the server via an AJAX call, then in the callback, update that table row saying done.
Initially i tried just firing off the 1000 ajax requests inside the .each selector, but the browser was locking up.
So i changed it to try and use an internal ajax counter, so only ever fire off 50 at a time.
Here's the code:
$('#do').click(function () {
var maxAjaxRequests = 50;
var ajaxRequests = 0;
var doneCounter = 0;
var toDo = $('#mytable tr').length;
$.each($('#mytable > tr'), function (i, v) {
while (doneCounter < toDo) {
if (ajaxRequests <= maxAjaxRequests) {
ajaxRequests++;
doAsyncStuff($(this), function () {
ajaxRequests--;
doneCounter++;
});
} else {
setTimeout(function() {
}, 1000);
}
}
});
});
function doAsyncStuff(tr, completeCallback) {
$.ajax({
url: '/somewhere',
type: 'POST',
dataType: 'json',
data: null,
contentType: 'application/json; charset=utf-8',
complete: function () {
completeCallback();
},
success: function (json) {
// update ui.
},
error: function (xmlHttpRequest, textStatus, errorThrown) {
// update ui.
}
});
}
But the browser is still being locked up. It never goes into the $.ajax complete callback, even though i can see the request coming back successfully (via Fiddler). Therefore its just sleeping, looping, sleeping, etc because the callback is never returned.
I've got a feeling that the entire doAsyncStuff function needs to be asynchronous?
Any ideas on what i am doing wrong (or how i can do this better)?
You are doing a while loop inside the .each callback function, so there is much more ajax request than 1000, the worst is 1000*1000.
You could delay each ajax request with different time.
$('#do').click(function () {
$('#mytable > tr').each(function (i, v) {
var $this = $(this);
setTimeout(function () {
doAsyncStuff($this, function () {
console.log('complete!');
});
}, i * 10);
});
});
The browser gets locked because of the WHILE... You are creating an endless loop.
The while loops runs over and over waiting for the doneCounter to be increased, but the javascript engine cannot execute the success call of the ajax since it is stuck in the while...
var callQueue = new Array();
$('#mytable > tr').each(function(key,elem){callQueue.push($(this));});
var asyncPageLoad = function(){
var tr = callQueue.splice(0,1);
$.ajax({
url: '/somewhere',
type: 'POST',
dataType: 'json',
data: null,
contentType: 'application/json; charset=utf-8',
complete: function () {
completeCallback();
asyncPageLoad();
},
success: function (json) {
// update ui.
},
error: function (xmlHttpRequest, textStatus, errorThrown) {
// update ui.
}
}
};
asyncPageLoad();
This will call the requests one by one. If you want, simply do a for() loop inside to make maybe 5 calls? And increase the amount if the browser is fine.
Actually, I prefer to send new request when current request is done. I used this method to dump db tables (in this work). Maybe it gives an idea.
See this link, check all check boxes and click Dump! button. And you can find the source codes here (see dumpAll function).
Related
In the below code I am making an API call to my backend node.js app using setTimeout() which calls my AJAX at every 5 seconds. Inside my AJAX success I am displaying divContent1 & divContent2 based on certain condition which should execute at least once. After that only divContent2 should be visible at each setTimeout() calls.
index.html
<script type="text/javascript">
$(document).ready(function(){
$.ajax({
url: "http://localhost:8070/api/route1",
type: 'POST',
dataType:'json',
success: function(res) {
//Some Task
}
});
$("#myButton").click(function(){
const route2 = function() {
$.ajax({
url: "http://localhost:8070/api/route2",
type: "POST",
dataType: "json",
data: { var1: val1 },
success: function (res) {
// Various tasks
if(res.flag){
$("#divContent1").hide();
$("#divContent2").show();
}
else{
$("#divContent1").show();
}
//Functions that handle div content data
},
beforeSend: function() {
$("#divContent1").hide();
$("#divContent2").hide();
},
complete: function() {
setTimeout(route2,5000);
},
});
};
$(function(){
route2();
})
});
});
</script>
The setTimeout() calls the entire route2 function which handles all the display and insertion of div content. However, the ask is to only display divContent2 from the second call.
Looking for a solution for this
The setTimeout() calls the entire route2 function which handles all
the display and insertion of div content. However, the ask is to only
display divContent2 from the second call.
You're calling route2 recursively with setTimeout(route2,5000); under complete. So this will run infinitely as complete occur each time an ajax call is completed (wether success or error). So what you can do is to create a timer and clear it after the second execution, something like this:
var ctr = 0, timer =0;
const route2 = function() {
$.ajax({
...
success: function (res) {
//Write you logic based on ctr
}
complete: function() {
if(ctr>0){
clearTimeout(timer)
}else{
timer = setTimeout(route2,5000);
ctr = ctr+ 1;
}
},
});
};
Will an external variable be enough? Just define it in the outer context and set/check it to choose the behavior:
// before declaring button click handler
var requestDoneAtLeastOnce = false;
// ...
// somewhere in success handler
success: function (res) {
if (!requestDoneAtLeastOnce) {
requestDoneAtLeastOnce = true;
// do something that belongs only to handling the first response
}
else {
// this is at least the second request, the other set of commands belongs here
}
}
I'm trying to call an ajax before user leaving a page, this what i have done so far. But it doesn't even hit the ajax page.
This is what i have done so far.
window.onbeforeunload = closeIt();
function closeIt()
{
var key="save-draft";
$.ajax({
url: "app/ajax_handler.php",
type:"GET",
data:{key:key},
success: function(data) {
return data;
}
});
}
I Have tried this one also both failed in my case.
$( window ).unload(function() {});
The only way I think is to let the user know that it's a process on background with a confirm message, that will block the exit until user click on Accept or you've got the response.
Something like that:
window.onbeforeunload = closeIt();
function closeIt()
{
/*var key="save-draft";
$.ajax({
url: "app/ajax_handler.php",
type:"GET",
data:{key:key},
success: function(data) {
return data;
}
});*/
setTimeout(function() {
return confirm("There is a process that isn't finished yet, you will lose some data. Are you sure you want to exit?");
}, 1000);
}
I'm trying to code some JavaScript with jQuery that executes some asynchronous events sequentially (in a loop); only iterating afte the previous async event has completed.
The basic idea is:
for (var i = 0; i < someLength; i++) {
// 1. dynamically add a <form> and <input>s to the DOM
// 2. submit the form to a target <iframe>
// 3. wait for an async callback indicating the form has been submitted
}
I have working code for #1 and #2, and I can attach a load event listener to the <iframe> to know when the form submit has completed:
$('.iframe').on('load', function() { ...
});
for (var i = 0; i < someLength; i++) {
// 1. dynamically add a <form> and <input>s in the DOM
// 2. submit the form to a target <iframe>
// 3. wait for an async callback indicating the form has been submitted
}
The problem is I don't know how to tie the ready callback to the loop logic. I tried to look into deferreds/promises, but didn't really see how to correctly apply those concepts here.
If the answer is to use promises, then I would love to also see how to incorporate some code to show a "loading" spinner while the loop is going, and then remove the spinner once we're out of the loop.
Thanks!
For-loop dislike asynchronous operations especially if you want to chain them. A solution may look like this.
$('.iframe').on('load', function() { ...
// increment i
//if(i >= someLength) exit
// 1. dynamically add a <form> and <input>s in the DOM
// 2. submit the form to a target <iframe>
});
//for (var i = 0; i < someLength; i++) {//no loop
//}
// 1. dynamically add a <form> and <input>s in the DOM
// 2. submit the form to a target <iframe>
// 3. nothing to wait
I think you can do it in recursive way instead of a for loop. something like this-
$("#imgSpinner").show();
someFunction(0,someLength);
function someFunction(currentSeq,totalIterations)
{
$.ajax({
url: URL,
type: 'POST',
contentType: 'application/json; charset=utf-8',
success: function (result) {
if (currentSeq<totalIterations)
someFunction(currentSeq++,totalIterations);
else
$("#imgSpinner").hide();
},
error: function (error) {
//handle error
}
});
}
I'm trying to understand how you can have a for-loop creating forms and fields... are all your forms containing the same fields? Ie multiple email addresses or something?
Without understanding the design, I'll give you this as an example of submitting some data then when that finishes submitting the next data.
$.when(AjaxSubmitFirstData.call()).done(function (data) {
$.when(AjaxSubmitSecondData.call()).done(function (data) {
// finished
});
});
var AjaxSubmitFirstData = {
call: function () {
return $.ajax({
url: url,
type: 'POST',
data: "{}",
contentType: 'application/json; charset=utf-8',
}).done(function (data) {
}).fail(function (jq, textStatus) {
});
}
};
var AjaxSubmitSecondData = {
call: function () {
return $.ajax({
url: url,
type: 'POST',
data: "{}",
contentType: 'application/json; charset=utf-8',
}).done(function (data) {
}).fail(function (jq, textStatus) {
});
}
};
I'm trying to fetch posts dynamically using AJAX and JQuery by checking if the user is close to the bottom. Serverside is in python on GAE.
Listening for scroll:
this.config.window.on('scroll',this.loadContent);
1.Checking for distance from bottom
2.Sending an ajax request with the number of current posts in order to retrieve the next 10
3.results.check = true means that the server has no further posts to send.
loadContent: function(){
// 1
if($(document).height() - $(window).height() - $(window).scrollTop() < 1000) {
var posts = $('.troll').children('div').length;
data = 'loadmore=True&offset=' + posts; //2
$.ajax({
url: '/',
type: 'POST',
data: data,
dataType: 'json',
success: function(results){
if (results.check === 'true'){ //3
$(window).unbind('scroll');
return;
}
Post.insert10Values(results);
}
});
};
},
insert10Values: function(results){
var update = Handlebars.compile($('#troll10').html()),
troll10update = update(results);
$('div.troll').append( troll10update );
}
The problem here is that when scrolling fast, two or more requests are sent to the server and i get duplicate entries. I want to rate-limit on client-side.
Set a flag loading = false. Before you send a request, check the flag. If it's false, set the flag to true and proceed with request, otherwise ignore the event. When results arrive, show them and set the flag back to false.
Part of your problem is scroll event will trigger many times a second
you can throttle any function calls doing something like this:
var scrollTimer=false;
var delay=500; /* 1/2 second*/
$(window).on('scroll',function(){
if( scrollTimer){
clearTimeout( scrollTimer);
}
scrollTimer=setTimeout(function(){
/* run your code here*/
}, delay);
});
As for the ajax you could store a time for last ajax call and set a miniumum difference based on now vs stored time before making a new ajax call
var lastAJAX=Date.now(), AJAXMin=5000;/* 5 seconds*/
function checkAJAXCalls(){
var now=Date.now(), diff=now-lastAJAX;
if( diff >= AJAXMin){
lastAJAX=now;
return true;
}else{
return false;
}
}
Then run if(checkAJAXCalls()) prior to making request. Concept could be modified to update lastAJAX in success callback of $.ajax also
jQuery.ajax has a method called beforeSend. It is executed right before your ajax call. You can use it to check if any other request is in progress and cancel the call if there is one. If you return false in beforeSend function, the ajax call will not be fired so you won't have any duplicate content.
$.ajax({
url: '/',
type: 'POST',
data: data,
dataType: 'json',
beforeSend: function() {
if (window.nextPageProcess) {
return false;
} else {
window.nextPageProcess = 1;
}
},
success: function(results){
if (results.check === 'true'){ //3
$(window).unbind('scroll');
return;
}
Post.insert10Values(results);
window.nextPageProcess = 1;
}
});
var refreshId_hxlatestposts = setInterval(function() {
var el = $("#hxlatestposts");
var req = $.get("example.php");
el.fadeOut('slow', function () {
req.done(function( data ){
el.html(data).fadeIn('slow');
});
});
}, 60000);
This is what i use to refresh a div every minute, sometimes it gets hung up when the site it is getting the feed from is down or something. I'd like to some how have a timeout so if it cannot load the php file in X seconds then return 'Fail to load'.
jQuery documentation (.ajaxSetup()) suggests using .ajaxSetup() to set the value for timeout, instead of using it in individual requests.
You can use request.fail() to register a function in case of a failed request.
$.ajaxSetup({
timeout: 5000
});
var refreshId_hxlatestposts = setInterval(function() {
var el = $("#hxlatestposts");
var req = $.get("example.php");
el.fadeOut('slow', function() {
req.done(function(data) {
el.html(data).fadeIn('slow');
});
req.fail(function(jqXHR, textStatus) {
el.html('Fail to load').fadeIn('slow');
});
});
}, 60000);
Nice use of deferred objects.
If you replace $.get with $.ajax, you can add a timeout.
var req = $.ajax({
url: "example.php",
type: "GET",
timeout: 5000 // 5 seconds
});
and then add a fail handler
req.done(function(){...}).fail(function(){
alert("failed to load");
});
You'll want to check the status of the incoming response to ensure that the service returned a 200 Ok status. This is more reliable than just waiting for a timeout-- you will know if it's good data or not an can decide to retry by putting your timeout in the complete functions.
$.ajax({
//...
success: function(data, textStatus, xhr) {
console.log(xhr.status);
//handle status codes etc.
// then set your timeout
},
complete: function(xhr, textStatus) {
console.log(xhr.status);
//handle status codes etc.
// then set your timeout
},
// OR
fail: function( xhr, textStatus ){
//retry code or timeout
}
});
jQuery's $.get is just a shorthand for $.ajax, which is used when more flexibility is required (in your case, yes)
Replace $.get("example.php"); with:
$.ajax({
type: "GET",
url: "example.php",
timeout: X*1000,
}).done(function(data) {
el.fadeOut('slow', function () {
el.html(data).fadeIn('slow');
});
}, 60000);
});
where X is number of seconds you would want it to wait (timeout)