How to start computation when entire UI is shown - javascript

Consider the simplest case -- show progress bar, start computation, close progress bar.
With such html piece:
<p id="hello" style="display:none">HELLO WORLD</p>
To my surprise this does not work:
function foo()
{
var hello = $('#hello');
hello.html(new Date().getTime());
hello.show();
setTimeout(function(){
var big = 0;
for (var i=0;i<10000000;++i)
if (Math.sqrt(i)>Math.cos(i)) // just to keep CPU busy
big = i;
console.log(i);
},0);
}
$(window).load(function ()
{
foo();
});
And using jQuery promise does not help as well:
hello.show().promise().done(function(){...
In both cases the element is shown (visually) at the same time as you have the output in console.
I wrote visually, because internally the element can be reported as already shown, but what user sees counts.

You can put your code for computing in separate javascript function, even its linear it wont wait for computing to get finished in javascript and move to next line immediately. I have put a wait before hiding the progress bar because you need to have it available for atleast a second.
function startComputing(){
var big = 0;
for (var i=0;i<10000000;++i)
if (Math.sqrt(i)>Math.cos(i)) // just to keep CPU busy
big = i;
console.log(i);
}
function foo()
{
var hello = $('#hello');
hello.html(new Date().getTime());
hello.show();
setTimeout(function(){startComputing();},500);
setTimeout(function(){hello.hide()},1000);
}

Related

unable to refresh DOM element while heavy javascript calculation goes

I want to refresh a span element before my calculations start to inform user that calculation was started.
the following code never displays 'calculating' message:
<script>
document.getElementById('text').innerHTML = 'calculating';
for (var i=0; i<9999;i++){
var y = Math.pow(i,i);
console.log(y);
}
document.getElementById('text').innerHTML = 'done';
</script>
</body>
</html>
how to fix that?
Guys, setTimeout is not an option for me. besides it looks ugly.
Place your code inside a setTimeout() call, and add a very minimal delay. I usually put 0ms, which just waits for the frame to render, then calls the function. Example:
document.getElementById('text').innerHTML = 'calculating';
setTimeout(function() {
for (var i=0; i<9999;i++){
var y = Math.pow(i,i);
console.log(y);
}
document.getElementById('text').innerHTML = 'done';
}, 0);
The first argument is a function to be called after the time passes, the second argument is the time to wait before calling the function. Note that this may still hang the browser if the calculation is too big (e.g. 999999 loop steps on a 2.5GHz i5)

Javascript/AJAX Asynchronous Loading Spinners

I am trying to make a basic enough page that allows the user to execute a php script by clicking a button. Each button will have a loading spinner popup on clicking.
My problem is, on clicking one button and then clicking another, both spinners close at the exact same time even though the second may still be processing.
Does anyone know how to make these spinners truly asynchronous ? Thanks so much in advance, its killing me.
JS:
function test(element){
var append = "#";
var test = append.concat(element);
document.getElementById(element).style.visibility='visible';
$.ajax({url:"test.php",success:function(result){
hide(element);
}
});
};
function hide(element){
document.getElementById(element).style.visibility='hidden';
};
</script>
HTML:
<html>
<?
$index = 0;
$myArray = array ("1", "2", "3", "4", "5");
for($index = 0; $index < 5; $index++){?>
<button onclick="test('<?echo $myArray [$index];?>')">Start</button>
<img id="<?echo $myArray [$index];?>" src="images/loader.gif"
style="visibility:hidden"/>
<br><br>
<?}?>
</html>
I would implement a counter. Each time you show the loading indicator, add one to the counter and each time you want to hide it, subtract one. Then monitor the counter and whenever it is above zero show the loading indicator and when at zero hide it. Make sense?
Something like the following (untested) code might do the trick and it neatly means you can avoid worrying about the spinner at all in ajax requests:
var spinningAjax = (function() { // use of the closure created by an immediate function gives us the scope to create a persistant counter variable
var counter = 0;
$(document).ajaxComplete(function() {
counter--;
if (counter === 0) {
showSpinner(false);
}
});
return function(settings) {
counter++;
showSpinner(true);
$.ajax(settings);
}
})();
var showSpinner(bool) {
// I'll leave this up to you as it looks like your posted html / js is for example purposes rather than replicating your actual site
};
EDIT: Ok, having seen the comments to another answer, I realise this doesn't quite solve the situation you're in. I'll have a think and see if I can do better
EDIT2: I think this (still untested, unfortunately) code may be what you require. Please let me know in the comments if you have any issues.
var spinningAjax = (function() { // closure of immediate function lets us create a persistant array of the counters for each spinner
var counter = []; // an array to hold the counters for each spinner
$(document).ajaxComplete(function(event, xhr, settings) { // called whenever any ajax request is completed
if (typeof settings.ajaxGroup !== 'undefined') { // only update the counters if an ajaxGroup has been provided
counter[settings.ajaxGroup]--;
if (counter[settings.ajaxGroup] === 0) {
showSpinner(false, settings.ajaxGroup); // hide spinner when all requests connected with the spinner have been completed
}
}
});
return function(settings) { // this is the function actually assigned to the variable spinningAjax as a result of the immediate function
counter[settings.ajaxGroup] = counter[settings.ajaxGroup] ? counter[settings.ajaxGroup]+1 : 1; // can't just use the ++ operator as this property might not be defined yet
showSpinner(true, settings.ajaxGroup);
$.ajax(settings);
}
})();
var showSpinner(bool, spinnerIdentifier) {
// I'll leave this up to you as it looks like your posted html / js is for example purposes rather than replicating your actual site
};

Javascript : setTimeout and interface freezing

Context
I've got about 10 complex graphs which take 5sec each to refresh. If I do a loop on these 10 graphs, it takes about 50 seconds to refresh. During these 50 seconds, the user can move a scrollbar. If the scrollbar is moved, the refresh must stop and when the scrollbar stops to move, the refresh occurs again.
I'm using the setTimeout function inside the loop to let the interface refresh.
the algorithm is :
render the first graph
setTimeout(render the second graph, 200)
when the second graph is rendered, render the third one in 200ms, and so on
The setTimeout allows us to catch the scrollbar event and to clearTimeout the next refresh to avoid to wait 50sec before moving the scrollbar...
The problem is that it does not run anytime.
Take the simple following code (you can try it in this fiddle : http://jsfiddle.net/BwNca/5/) :
HTML :
<div id="test" style="width: 300px;height:300px; background-color: red;">
</div>
<input type="text" id="value" />
<input type="text" id="value2" />
Javascript :
var i = 0;
var j = 0;
var timeout;
var clicked = false;
// simulate the scrollbar update : each time mouse move is equivalent to a scrollbar move
document.getElementById("test").onmousemove = function() {
// ignore first move (because onclick send a mousemove event)
if (clicked) {
clicked = false;
return;
}
document.getElementById("value").value = i++;
clearTimeout(timeout);
}
// a click simulates the drawing of the graphs
document.getElementById("test").onclick = function() {
// ignore multiple click
if (clicked) return;
complexAlgorithm(1000);
clicked = true;
}
// simulate a complexe algorithm which takes some time to execute (the graph drawing)
function complexAlgorithm(milliseconds) {
var start = new Date().getTime();
for (var i = 0; i < 1e7; i++) {
if ((new Date().getTime() - start) > milliseconds){
break;
}
}
document.getElementById("value2").value = j++;
// launch the next graph drawing
timeout = setTimeout(function() {complexAlgorithm(1000);}, 1);
}
The code does :
when you move your mouse into the red div, it updates a counter
when you click on the red div, it simulates a big processing of 1sec (so it freezes the interface due to javascript mono thread)
after the freezing, wait 1ms, and resimulate the processing and so on until the mouse move again
when the mouse move again, it breaks the timeout to avoid infinite loop.
The problem
When you click one time and move the mouse during the freeze, I was thinking that the next code that will be executed when a setTimeout will occurs is the code of the mousemove event (and so it will cancel the timeout and the freeze) BUT sometimes the counter of click gains 2 or more points instead of gaining only 1 point due to the mouvemove event...
Conclusion of this test : the setTimeout function does not always release resource to execute a code during a mousemove event but sometimes kept the thread and execute the code inside the settimeout callback before executing another code.
The impact of this is that in our real example, the user can wait 10 sec (2 graphs are rendered) instead of waiting 5 seconds before using the scrollbar. This is very annoying and we need to avoid this and to be sure that only one graph is rendered (and other canceled) when the scrollbar is moved during a render phase.
How to be sure to break the timeout when the mouse move ?
PS: in the simple example below, if you update the timeout with 200ms, all runs perfectly but it is not an acceptable solution (the real problem is more complex and the problem occurs with a 200ms timer and a complex interface). Please do not provide a solution as "optimize the render of the graphs", this is not the problem here.
EDIT : cernunnos has a better explanation of the problem :
Also, by "blocking" the process on your loop you are ensuring no event can be handled until that loop has finished, so any event will only be handled (and the timeout cleared) inbetween the execution of each loop (hence why you sometimes have to wait for 2 or more full executions before interrupting).
The problem is exactly contains in bold words : I want to be sure to interrupt the execution when I want and not to wait 2 or more full executions before interrupting
Second EDIT :
In summary : takes this jsfiddle : http://jsfiddle.net/BwNca/5/ (the code above).
Update this jsfiddle and provide a solution to :
Mouse move on the red div. Then click and continue moving : the right counter must raise only once. But sometimes it raises 2 or 3 times before the first counter can run again... this is the problem, it must raise only once !
The BIG problem here is setTimeout is unpredictable once it started, and especially when it is doing some heavy lifiting.
You can see the demo here:
http://jsfiddle.net/wao20/C9WBg/
var secTmr = setTimeout(function(){
$('#display').append('Timeout Cleared > ');
clearTimeout(secTmr);
// this will always shown
$('#display').append('I\'m still here! ');
}, 100);
There are two things you can do to minimize the impact on the browser performance.
Store all the intances of the setTimeoutID, and loop through it when you want to stop
var timers = []
// When start the worker thread
timers.push( setTimeout(function () { sleep(1000);}, 1) );
// When you try to clear
while (timers.length > 0) {
clearTimeout(timers.pop());
}
Set a flag when you try to stop process and check that flag inside your worker thread just in case clearTimeout failed to stop the timer
// Your flag
var STOPForTheLoveOfGod = false;
// When you try to stop
STOPForTheLoveOfGod = true;
while (timers.length > 0) {
clearTimeout(timers.pop());
}
// Inside the for loop in the sleep function
function sleep(milliseconds) {
var start = new Date().getTime();
for (var i = 0; i < 1e7; i++) {
if (STOPForTheLoveOfGod) {
break;
}
// ...
}
}
You can try out this new script.
http://jsfiddle.net/wao20/7PPpS/4/
I may have understood the problem but assuming you are trying to block the interface after a click for a minimum of 1 second and unblocking it by moving the mouse (after that 1 second minimum):
This is not a good implementation of sleep, as you are keeping the process running the whole time (doing nothing != sleeping), this results in a waste of resources.
Why not create an overlay (a semi/fully transparent div), put it on top of the rest of the interface (position fixed, full width and full height) and use it to prevent any interaction with the underlying interface. Then destroy it when the conditions are right (a second has passed and the user moved the mouse).
This behaves more like a sleep (has some initial processing time but then releases the processor for a given amount of time) and should help you achieve the behavior you need (assuming i understood it right).
It has the added bonus of allowing you to give the user some visual cue that some processing is being done.
Edit:
Also, by "blocking" the process on your loop you are ensuring no event can be handled until that loop has finished, so any event will only be handled (and the timeout cleared) inbetween the execution of each loop (hence why you sometimes have to wait for 2 or more full executions before interrupting).
Surprising enough you have not figured out that, when you setTimeout(); you can input a check after that. A variable is true then trash the wait, or trash it. Now there is a method that you can check to scroll with a scroll bar. After you have checked it true inside a variabled using the means, then you will find this will repeat inifite times as they scroll the bar, making many executing times of 5 seconds. To fix this add a 1 second wait to make sure it doesn't over repeat. Your welcome :)
Any long-running function is going to tie up your browser window. Consider moving your complexAlgorithm() outside of your main javascript code using WebWorkers.
The answer is in your question
...the refresh must stop and when the scrollbar stops to move, the
refresh occurs again.
You should write complexAlgorithm in such way that you can almost instantly brake it in a middle (just when you know you will have to re run)
so main code should look something like
stopAllRefresh; //should instantly(or after completing small chunk) stop refresh
setTimeout(startRefresh, 100);
and render graph in small chunks (each runs < 1sec) in setTimeout
like
var curentGraph = 0;
var curentChunk = 0;
function renderGraphChunk(){
if (needToBreak) //check if break rendering
{exit};
// Render chunk here
render(curentGraph, curentChunk);
curentChunk +=1;
setTimeout(renderGraphChunk, 1);
}
this is just a idea sketch, real implementation can be completely different
What you want to do can not be done without web worker, that is only implemented in some latest browser specially Chrome.
Otherwise, you have to break your algorithm in queue. Just like jQuery UI puts every next animation calculation in queue. http://api.jquery.com/jQuery.queue/
It is a simple queue and next instruction set is queued with help of setTimeout.
for (i=0; i <1000; i++)
{
process (i) ;
}
Can be translated to
function queue(s,n, f)
{
this.i=s;
this.n=n;
this.f=f;
this.step = function(){
if ( this.i <this.n)
{
this.f(this.i);
this.i = this.i +1;
var t = this;
setTimeout( function ( ) { t.step(); } , 5);
}
}
this.step();
}
queue ( O, 1000, function(i){
process(i);
}) ;
This is just an example of how Synchronous for loop can be written to execute same logic asynchronously using smaller independent iteration.
Try and check out web workers. I think it will be useful in this situation.
http://en.wikipedia.org/wiki/Web_worker
http://www.html5rocks.com/en/tutorials/workers/basics/

Adding text periodically

I am trying to run small snippet code in JavaScript, where I want to write on the web page simple hello world each 5 seconds. I think it must be ok, but no, still I got only first hello world and no more. Could you give me a hand in this? Thanks
<script type="text/javascript">
var i=0;
function startTimer() {
window.setTimeout('refresh()',5000);
}
function refresh() {
document.write("Hello world "+i+"<br/>");
i++;
window.setTimeout('startTimer()',1);
}
startTimer();
</script>
NOTE: As Amar Palsapure has noted in this answer, the root cause of the problem was the use of document.write. In my demonstration, I use a p element to document.body.appendChild() to add the text to the screen.
You can use setTimeout(), but you have to make it contingent on the last setTimeout() that ran; so that each time the caller runs, it creates the next timeout.
setInterval() is designed to run at a "regular" interval (neither setTimeout() nor setInterval() are truly reliable in when they run); however, if the calls to setInterval() get backed up due to some other process blocking it's execution (Javascript is single-threaded), you could have issues with those queued callbacks. That's why I prefer the approach I have below.
Note, refrain from the setTimeout('funcCalled()', 100) usage; this is running an eval() on that string you're passing in, which can change the scope in which you're running the callback, as well as being considered "evil" due to security issues related to eval(). You're best to avoid it altogether.
EDIT - Modified slightly.
I have made some changes to the approach. See my comments.
// The first and last lines comprise a self-executing,
// anonymous function, eg, (function(){})();.
// This allows me to use a local function scope and not the
// global window scope, while still maintaining my variables
// due to it being a "closure" (function(){}).
(function(){
var i = 0,
timer = 5000,
// I'm just going to add this to the DOM.
text = document.createElement('p');
// This is a variable function, meaning it stores a
// reference to a function.
var helloWorld = function() {
// Here is where I add the Hello World statement
text.innerHTML += 'Hello World! Loop: ' + i++ + '<br/>';
// Them add it to the DOM.
document.body.appendChild(text);
// I added this so it wouldn't run forever.
if (i < 100) {
// A setTimeout() will be added each time the last
// was run, as long as i < 100.
// Note how I handle the callback, which is the
// first argument in the function call.
setTimeout(helloWorld, timer);
}
// I added the change so it wouldn't take so long
// to see if was working.
timer = 500;
}
// Here I use a variable function and attach it to the
// onload page event, so it will run when the page is
// done loading.
window.onload = helloWorld;
})();
http://jsfiddle.net/tXFrf/2/
The main issue is document.write. There is nothing wrong with setTimeout or rest of the code.
The reason it does not work is that once document.write is called the first time, it overwrites your existing code of setTimeout() and since there is no code so it will not work.
What you need to do is use some other means to write the value in the page, certainly no document.write...
Instead of using setInterval use setTimeout.
You can try this
<html>
<body>
<div id="clock" ></div>
<script type="text/javascript">
var i = 0,
timerHandle,
clock;
function startTimer() {
clock = document.getElementById('clock');
//You can use timerHandle, to stop timer by doing clearInterval(timerHandle)
timerHandle = self.setInterval(funRefresh, 2000);
}
var funRefresh = function refresh() {
clock.innerHTML += "Hello world " + i++ + "<br/>";
}
startTimer();
</script>
</body>
</html>
Hope this helps you.
Here is the working Code
var i = 0;
function startTimer() {
window.setInterval(refresh, 5000);
}
function refresh() {
document.write("Hello world " + i + "<br/>");
i++;
// window.setTimeout(startTimer,1);
}
startTimer();​

How many timers in a window? [duplicate]

I have to use atleast 2 setTimeouts and 1 setInterval. Does this have any dependency on the browser or javascript engine being used?
tl;dr: Don't worry about the cost of timers until you're creating 100K's of them.
I just did a quick test of timer performance by creating this test file (creates 100K timers over and over):
<script>
var n = 0; // Counter used to verify all timers fire
function makeTimers() {
var start = Date.now();
for (var i = 0; i < 100000; i++, n++) {
setTimeout(hello, 5000);
}
console.log('Timers made in', Date.now() - start, 'msecs');
}
function hello() {
if (--n == 0) {
console.log('All timers fired');
makeTimers(); // Do it again!
}
}
setTimeout(makeTimers, 10000); // Wait a bit before starting test
</script>
I opened this file in Google Chrome (v54) on my circa ~2014 Macbook Pro, and went to the Timeline tab in Developer Tools and recorded the memory profile as the page loaded and ran thru 3-4 cycles of the test.
Observations
The timer creation loop takes 200ms. The page heap size starts at 3.5MB pre-test, and levels out at 3.9MB.
Conclusion
Each timer takes ~.002 msecs to set up, and adds about 35 bytes to the JS heap.
On a page you can have as many setTimeouts/setIntervals running at once as you wish, however in order to control each individually you will need to assign them to a variable.
var interval_1 = setInterval("callFunc1();",2000);
var interval_2 = setInterval("callFunc2();",1000);
clearInterval(interval_1);
The same code above applies to setTimeout, simply replacing the wording.
As Kevin has stated, JavaScript is indeed single threaded, so while you can have multiple timers ticking at once, only one can fire at any one time - i.e. if you have one that fires a function which 'halts' in execution, for example with an alert box, then that JS must be 'resumed' before another can trigger I believe.
One further example is given below. While the markup is not valid, it shows how timeouts work.
<html>
<body>
<script type="text/javascript">
function addThing(){
var newEle = document.createElement("div");
newEle.innerHTML = "Timer1 Tick";
document.body.appendChild(newEle);
}
var t1= setInterval("addThing();",1000);
var t2 = setInterval("alert('moo');",2000);
</script>
</body>
</html>
You can use as many as you want. Just remember that JavaScript is single threaded, so none of them can execute in parallel.
var interval_1 = setInterval("callFunc1();",2000); calls eval() which is evil so it's BAD.
Use this instead var interval_1 = setInterval(callFunc1,2000);
And for the question, you may use as many as you want but if all have the same interval between two actions, you better do it this way
var interval = setInterval(function() {
// function1
fct1();
// function2
fct2();
},2000);

Categories

Resources