force DOM redraw with javascript on demand - javascript

The title of the question expresses what I think is the ultimate question behind my particular case.
My case:
Inside a click handler, I want to make an image visible (a 'loading' animation) right before a busy function starts. Then I want to make it invisible again after the function has completed.
Instead of what I expected I realize that the image never becomes visible. I guess that this is due to the browser waiting for the handler to end, before it can do any redrawing (I am sure there are good performance reasons for that).
The code (also in this fiddle: http://jsfiddle.net/JLmh4/2/)
html:
<img id="kitty" src="http://placekitten.com/50/50" style="display:none">
<div>click to see the cat </div>
js:
$(document).ready(function(){
$('#enlace').click(function(){
var kitty = $('#kitty');
kitty.css('display','block');
// see: http://unixpapa.com/js/sleep.html
function sleepStupidly(usec)
{
var endtime= new Date().getTime() + usec;
while (new Date().getTime() < endtime)
;
}
// simulates bussy proccess, calling some function...
sleepStupidly(4000);
// when this triggers the img style do refresh!
// but not before
alert('now you do see it');
kitty.css('display','none');
});
});
I have added the alert call right after the sleepStupidly function to show that in that moment of rest, the browser does redraw, but not before. I innocently expected it to redraw right after setting the 'display' to 'block';
For the record, I have also tried appending html tags, or swapping css classes, instead of the image showing and hiding in this code. Same result.
After all my research I think that what I would need is the ability to force the browser to redraw and stop every other thing until then.
Is it possible? Is it possible in a crossbrowser way? Some plugin I wasn't able to find maybe...?
I thought that maybe something like 'jquery css callback' (as in this question: In JQuery, Is it possible to get callback function after setting new css rule?) would do the trick ... but that doesn't exist.
I have also tried to separte the showing, function call and hiding in different handlers for the same event ... but nothing. Also adding a setTimeout to delay the execution of the function (as recommended here: Force DOM refresh in JavaScript).
Thanks and I hope it also helps others.
javier
EDIT (after setting my preferred answer):
Just to further explain why I selected the window.setTimeout strategy.
In my real use case I have realized that in order to give the browser time enough to redraw the page, I had to give it about 1000 milliseconds (much more than the 50 for the fiddle example). This I believe is due to a deeper DOM tree (in fact, unnecessarily deep).
The setTimeout let approach lets you do that.

Use JQuery show and hide callbacks (or other way to display something like fadeIn/fadeOut).
http://jsfiddle.net/JLmh4/3/
$(document).ready(function () {
$('#enlace').click(function () {
var kitty = $('#kitty');
// see: http://unixpapa.com/js/sleep.html
function sleepStupidly(usec) {
var endtime = new Date().getTime() + usec;
while (new Date().getTime() < endtime);
}
kitty.show(function () {
// simulates bussy proccess, calling some function...
sleepStupidly(4000);
// when this triggers the img style do refresh!
// but not before
alert('now you do see it');
kitty.hide();
});
});
});

Use window.setTimeout() with some short unnoticeable delay to run slow function:
$(document).ready(function() {
$('#enlace').click(function() {
showImage();
window.setTimeout(function() {
sleepStupidly(4000);
alert('now you do see it');
hideImage();
}, 50);
});
});
Live demo

To force redraw, you can use offsetHeight or getComputedStyle().
var foo = window.getComputedStyle(el, null);
or
var bar = el.offsetHeight;
"el" being a DOM element

I do not know if this works in your case (as I have not tested it), but when manipulating CSS with JavaScript/jQuery it is sometimes necessary to force redrawing of a specific element to make changes take effect.
This is done by simply requesting a CSS property.
In your case, I would try putting a kitty.position().left; before the function call prior to messing with setTimeout.

What worked for me is setting the following:
$(element).css('display','none');
After that you can do whatever you want, and eventually you want to do:
$(element).css('display','block');

Related

setTimeout 0 and blocking function issues in Firefox

I came across a situation were a button event handler calls a function, that may take a couple seconds to complete depending on the input. Once the function completes, the output will show up in a grid.
The function is completely client side. Right before the function is running I add a css class to the grid wrapper div that basically just shows a 'loading' gif/animation.
This works fine in Chrome, but not in Firefox and IE 11.
Below is an oversimplified version of how I achieve this with javascript setTimeout 0.
$('#calc').on('click', function(){
$('#container').addClass('loading');
calculate(10, function(res){
$('#result').text(res);
$('#container').removeClass('loading');
});
});
//represents my long running function
function fib(n) {
if(n<2) {
return n;
}
return fib(n-2) + fib(n-1);
}
//will be called by click handler
function calculate(n,cb) {
setTimeout(function(){
var result = fib(n);
return cb(result);
},0)
}
As you can see I use setTimeout 0 in calculate(n,cb) to give the browser the ability to show the 'loading' animation before the function starts and then remove it when it is done.
However, this does not work in Firefox.
What are some other options for me to achieve what I am trying to do?
I am using jQuery here, but the actual project I am working on is using Angular5. But the idea should be the same.
Here is a jsFiddle to show what I am trying to do. Using the loading animation by Mattln4D (thanks)
https://jsfiddle.net/alabianc/qL5zggh7/
If you want to see some actual good result, run it with 40 as an input in calculate, but no more than that!
I appreciate any help!
I think if you set the timeout = 0, it is so fast to browser can show the loading animation. When I try to change timeout = 10 or 100, I can see the loading animation show on both of chrome, ff.

addEventListener to div element

I am trying to fire a script when the contents of a div are altered, specifically when a div receives the next set of results from a js loaded paginator.
I have this:
<script script type="text/javascript" language="javascript">
document.addEventListener("DOMCharacterDataModified", ssdOnloadEvents, false);
function ssdOnloadEvents (evt) {
var jsInitChecktimer = setInterval (checkForJS_Finish, 111);
function checkForJS_Finish () {
if ( document.querySelector ("#tester")
) {
clearInterval (jsInitChecktimer);
//do the actual work
var reqs = document.getElementById('requests');
var reqVal = reqs.get('value');
var buttons = $$('.clicker');
Array.each(buttons, function(va, index){
alert(va.get('value'));
});
}
}
}
</script>
This works well when the doc loads (as the results take a few seconds to arrive) but I need to narrow this down to the actual div contents, so other changes on the page do not fire the events.
I have tried:
var textNode = document.getElementById("sitepage_content_content");
textNode.addEventListener("DOMCharacterDataModified", function(evt) {
alert("Text changed");
}, false);
But the above does not return anything.
Can what I am trying to do be done in this way? If yes where am I going wrong?
Using Social Engine (Zend) framework with MooTools.
I did this in the end with a little cheat :-(
There is a google map loading on the page that sets markers to match the location of the results. So I added my events to the end this code namely: function setMarker() {}.
I will not mark this as the correct answer as it is not really an answer to my question, but rather a solution to my problem, which is localised to the Social engine framework.
I will add a Social engine tag to my original question in the hope it may help someone else in the future.
Thanks guys.

Trigger event on animation complete (no control over animation)

I've a scenario that requires me to detect animation stop of a periodically animated element and trigger a function. I've no control over the element's animation. The animation can be dynamic so I can't use clever setTimeout.
Long Story
The simplified form of the problem is that I'm using a third party jQuery sliding banners plugin that uses some obfuscated JavaScript to slide banners in and out. I'm in need of figuring out a hook on slideComplete sort of event, but all I have is an element id. Take this jsfiddle as an example and imagine that the javascript has been obfuscated. I need to trigger a function when the red box reaches the extremes and stops.
I'm aware of the :animated pseudo selector but I think it will need me to constantly poll the required element. I've gone through this, this, and this, but no avail. I've checked jquery promise but I couldn't figure out to use that in this scenario. This SO question is closest to my requirements but it has no answers.
P.S. Some more information that might be helpful:
The element isn't created by JavaScript, it is present on page load.
I've control over when to apply the plugin (that makes it periodically sliding banner) on the element
Most of the slideshow plugins I have used use changing classes at the end of the animation... You could extend the "addClass" method of jQuery to allow you to capture the class change as long as the plugin you use is using that method like it should:
(function($){
$.each(["addClass","removeClass"],function(i,methodname){
var oldmethod = $.fn[methodname];
$.fn[methodname] = function(){
oldmethod.apply( this, arguments );
this.trigger(methodname+"change");
return this;
}
});
})(jQuery);
I threw together a fiddle here
Even with obfuscated code you should be able to use this method to check how they are sending in the arguments to animate (I use the "options" object when I send arguments to animate usually) and wrap their callback function in an anonymous function that triggers an event...
like this fiddle
Here is the relevant block of script:
(function($){
$.each(["animate"],function(i,methodname){
var oldmethod = $.fn[methodname];
$.fn[methodname] = function(){
var args=arguments;
that=this;
var oldcall=args[2];
args[2]=function(){
oldcall();
console.log("slideFinish");
}
oldmethod.apply( this, args );
return this;
}
});
})(jQuery);
Well since you didn't give any indication as to what kind of animation is being done, I'm going to assume that its a horizontal/vertical translation, although I think this could be applied to other effects as well. Because I don't know how the animation is being accomplished, a setInterval evaluation would be the only way I can guess at how to do this.
var prevPos = 0;
var isAnimating = setInterval(function(){
if($(YOUROBJECT).css('top') == prevPos){
//logic here
}
else{
prevPos = $(YOUROBJECT).css('top');
}
},500);
That will evaluate the vertical position of the object every .5 seconds, and if the current vertical position is equal to the one taken .5 seconds ago, it will assume that animation has stopped and you can execute some code.
edit --
just noticed your jsfiddle had a horizontal translation, so the code for your jsfiddle is here http://jsfiddle.net/wZbNA/3/

how to repaint all the UI componenets in Jquery

I have a several divs connected to one another using the endpoint connections to one another. As I do a zoom in or zoom out, I need to repaint all the UI components. The UI components are drawn using the jsPlumb library(jquery/javascript based). There is a method in jsplumb which forces the repaint but it is not working as the way I want it to do. Here it is what I am trying to do.
$("div#explanation .plus").click(function(){
jsPlumb.repaintEverything();
var strongFont = parseFloat($("div.window strong").css('font-size'));
var newStrongFont = strongFont + 2;
$("div.window ").animate({
'height':'+=20px', 'width':'+=20px'
},"medium");
$("div.window strong").animate({
fontSize:newStrongFont
},"medium");
//This is not working
jsPlumb.repaintEverything();
jsPlumb.repaintEverything();
//I am calling here another function to repaint the div windows one by one
repaintWindows();
});
var repaintWindows = function(){
var jjl;
for(jjl=1;jjl<=xmlLength;jjl++)
{
var windo = "window"+jjl;
//alert("Window is ::"+windo);
jsPlumb.repaint(windo);
alert("Window is ::"+windo);
//_addEndpoints(wind, ["LeftMiddle", "BottomCenter"], ["TopCenter", "RightMiddle"]);
}
alert("the value of jjl is ::"+jjl+" \nThe value of xmlLength is::"+xmlLength);
};
The problem here is if I remove the
//alert("Window is ::"+windo);
from the repaintWindows method for loop, the windows get repainted during the next cycle of call. I want the repaint to work at the same time. If I keep the alert, then it does repaint the window at the same time. As well, at the end I dont want any kind of alert over there.
Can somebody please tell me where am I going wrong.
Any help is appreciated.
Thanks!
not sure, but try this one
$(window).resize(function() {
jsPlumb.repaintEverything();
});

Can't see problem in JS

I want that when mouse is over an image, an event should be triggered ONCE, and it should be triggered again only after mouse is out of that image and back again, and also at least 2 seconds passed.
If I leave my mouse over the image,it gets called like every milisecond,and by the logic of my function once you hover on the variable 'canhover' becomes 0 until you move mouse out
This code seems to have a bug and I cant see it. I need a new pair of eyes, but the algorithm is kinda logical
Working code :
<script type="text/javascript">
var timeok = 1;
function redotimeok() {
timeok = 1;
}
//
function onmenter()
{
if (timeok == 1)
{
enter();
timeok = 0;
}
}
//
function onmleave()
{
setTimeout(redotimeok, 2000);
leave();
}
//
$('#cashrefresh').hover(onmenter,onmleave);
function enter(){
$("#showname").load('./includes/do_name.inc.php');
$("#cashrefresh").attr("src","images/reficonani.gif");
}
function leave(){
$("#cashrefresh").attr("src","images/reficon.png");
}
</script>
I don't know if this will solve your entire problem (since we don't have a detailed description of what it is), but instead of:
$('#cashrefresh').hover(onmenter(),onmleave());
try:
$('#cashrefresh').hover(onmenter,onmleave);
And the same thing here:
setTimeout(redotimeok, 2000); // just the function name
Also, I don't see where you ever set timeok to zero. Do you mean to set timeok = 0 in onmenter()?
There are two methods in jquery for your problem:
.mouseenter() and .mouseleave()
Check out the demos there.
EDIT:
I thought hover was for mouseover and mouseout, sorry for confusion.
I checked your code again. And it seems that you're changing the image when mouse gets over the image, which forces browser to load the new image and the old image disappears for a very little while till the new one appears and i think this must be triggering both handlers continuosly and you're getting this behaviour.
Try not to change the source of the image, comment out that line and instead console.log("some message") there and see if the message is repeated as much as .load() was fired before.
Hope this helps.
Try changing onmleave function as follows:
function onmleave()
{
setTimeout(redotimeok, 2000);
leave();
}

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