I have a JS function which is triggered on a click event.
At the very first line in the function, I add a class to a html element. The html is a custom loader, and the class just makes the loader visible.
The problem is that the loader does not appear until the script has actually finished executing. The class is set on the element right after the script starts, but nothing visually happens in my browser until the script has finished executing.
$('body').on('click', '#button', function(){
$('#loader').addClass('active');
$('.fields').each(function(i, el){
// does some intensive stuff, including appending elements to a dom fragment, triggering events programmatically. This takes 5-10s to execute.
});
// the loader only appears visible in the browser once the code executed in the loop finishes.
});
The CSS in the active class is:
.active{
z-index: 9999;
display: block;
position: absolute;
left: 40%;
left: calc(50% - 18px);
left: -webkit-calc(50% - 18px);
top: 40%;
}
I tried do re-search this issue, but I couldn't find anything on google.
Maybe it's because I do not know what keywords I should search, I am not sure what is causing or how to refer to this issue.
So guys, you are my last hope. Could you point me in the right direction on how to debug or what is causing this?
If I add the fields loop inside a setTimeout function with 0 timeout, it works. But the idea is to fix it the correct way, and understand why it's not working as expected.
If I add the fields loop inside a setTimeout function with 0 timeout, it works.
This is a sensible approach, although requestAnimationFrame is stylistically slightly nicer.
But the idea is to fix it the correct way, and understand why it's not working as expected.
The browser won't trigger a repaint until the function has finished running - otherwise, it would do a repaint for every individual DOM modification, which would be expensive.
Related
I have a very large and complicated jQuery plugin which I will avoid posting here for simplicity's sake. My problem is very simple, and I will reduce it only to the relevant code:
I have a click event attached to a set of buttons:
$("ul.tick-boxes button").click(function(event) {
event.preventDefault();
$("ul.product-grid").addClass("loading");
$(this).toggleClass("active");
$theElement.trigger("filterOptionsChanged");
});
If you go to this link, you can see these in action in the left sidebar:
http://mazer.com/collections/refrigerator?preview_theme_id=22019779
Here is the css that produces a check-mark when you click the buttons:
ul.tick-boxes button.active .tick-box::after {
content: "\e603";
font-family: "custom-icons";
color: #51425d;
top: 2px;
left: 2px;
font-size: 0.75rem;
position: absolute;
}
If your computer is as slow as mine, then when you click these filter options, it takes a second or so to "tick" the "tick-box". If you can't see it, try unticking it, which for me takes noticeably longer. The time-point where the "tick" visibly renders is always simultaneous with the product-grid rebuilding and rendering. I haven't posted the code for manipulating the product-grid, but you can know that the line $theElement.trigger("filterOptionsChanged") triggers a lot of array and object processing to build a document fragment of the new product list, and updates the DOM at the end. I understand this can take a second, that is not my problem. But what I don't understand is why my "tick-boxes" are waiting until after the code of that event is finished to render. According to my css, all I need is a class active on the button, and that code is fired one line above triggering the "filterOptionsChanged" event, so it should fire before any product grid changes happen.
Now. If I open up my inspector in chrome, I can actually see the active classes toggling instantaneously on click, before the product grid updates. However, the css which adds the tick doesn't catch the active class on the element until after my "filterOptionsChanged" code completes.
My first attempt to solve the problem will be posted below. I read a good bit about the "expensiveness" of css pseudo-selectors. That essentially to a browser, it is like a dom manipulation every time an ::after element is created. So I then write this css:
ul.tick-boxes button .tick-box::after {
content: "\e603";
font-family: "custom-icons";
color: #51425d;
top: 2px;
left: 2px;
font-size: 0.75rem;
position: absolute;
opacity: 0;
}
ul.tick-boxes button.active .tick-box::after {
opacity: 1;
}
So now an ::after element always exists from the beginning, any rendering costs are paid for at the outset, so my thought was, now when I click this button, the tick is already there, we are just giving it an opacity of 1. Didn't fix the delay.
Now, I try removing the "filterOptionsChanged" event trigger entirely. This makes my whole sorting plugin stop working, but I don't care at this point, because I want to understand what is causing the problem. When I do remove that event trigger, the buttons and css render snappy. No more problems.
I have a vague thought that, ok, if a click event can be snappy without that event trigger, I need a way of seperating the two. First add the active class, then trigger "filterOptionsChanged". I think, ok, jQuery Deferreds. Here is that code:
$("ul.tick-boxes button").click(function(event) {
event.preventDefault();
var showLoading = jQuery.Deferred();
$("ul.product-grid").addClass("loading");
$(this).toggleClass("active");
showLoading.resolve();
$.when(showLoading).done(function() {
$theElement.trigger("filterOptionsChanged");
});
});
So showLoading is a blank Deferred, I then add my classes for the tick boxes to show, then I resolve the deferred. Now I say, when showLoading is done, then do the whole product-grid manipulation. Don't do these at the same time, javascript, wait for one to finish, then do the other. Still no avail. Any ideas?
According to this, all function calls in JavaScript block the UI until they complete; I'd wager that this includes the original function call to start the click event. A cheap solution might be to replace the trigger with something like:
setTimeout(function() { $theElement.trigger("filterOptionsChanged"); }, 200);
Which will hopefully delay the trigger long enough for the browser to repaint the UI (you could/should add a little loading icon in the original function, then remove it in the timeout). You could also take a look at web workers, which look like they're pretty much threads.
Try this,
CSS:
ul.tick-boxes button.active .tick-box::after {
content: "\e603";
font-family: "custom-icons";
color: #51425d;
top: 2px;
left: 2px;
font-size: 0.75rem;
position: absolute;
}
JS:
$("ul.tick-boxes button").click(function(event) {
event.preventDefault();
$("ul.product-grid").addClass("loading");
$(this).toggleClass("active").fadeIn(10, function () {
$theElement.trigger("filterOptionsChanged");
});
});
Using callback to delay the triggering. See if this work for you.
This is currently happening in chrome, in firefox I haven't had this issue (yet).
Here is a VERY simplified version of my problem.
HTML:
<div class="thumbnail">
Click me!
</div>
CSS:
div {
width: 200px;
height: 300px;
background-color: purple;
}
a {
position: absolute;
}
#media (max-width: 991px) {
div {
height: 200px;
}
}
Javascript:
$(document).ready(function () {
var $parent = $('#clickMe').parent();
function resize() {
$('#clickMe').offset({
top: $parent.offset().top + $parent.height()-$('#clickMe').height()
});
}
$(window).on('resize', resize);
resize();
});
The problem:
So what does this give when I resize (without dragging)? Well javascript launches first and sets the position of the <a></a> , then CSS applies the height change if we are < 992 px.
Logically the button is now visually at the outside of the div and not on the border like I had originally defined it to be.
Temporary solution proposed in this post.
jQuery - how to wait for the 'end' of 'resize' event and only then perform an action?
var doit;
$(window).on('resize', function(){ clearTimeout(doit); doit = setTimeout(resize, 500); });
Temporary solution is not what I'm looking for:
However, in my situation I don't really need to only call 'resize' when the resizing event is actually done. I just want my javascript to run after the css is finished loading/ or finished with it's changes. And it just feels super slow using that function to 'randomely' run the JS when the css might be finished.
The question:
Is there a solution to this? Anyone know of a technique in js to wait till css is completely done applying the modifications during a resize?
Additional Information:
Testing this in jsfiddle will most likely not give you the same outcome as I. My css file has many lines, and I'am using Twitter Bootstrap. These two take up a lot of ressources, slowing down the css application (I think, tell me if I'm wrong).
Miljan Puzović - proposed a solution by loading css files via js, and then apply js changes when the js event on css ends.
I think that these simple three steps will achieve the intended behavior (please read it carefully: I also suggest to read more about the mentioned attributes to deeply understand how it works):
Responsive and fluid layout issues should always be primarily (if not scrictly) resolved with CSS.
So, remove all of your JavaScript code.
You have positioned the inner a#clickMe element absolutely.
This means that it will be positioned within its closest relatively positioned element. By the style provided, it will be positioned within the body element, since there is no position: relative; in any other element (the default position value is static). By the script provided, it seems that it should be positioned within its direct parent container. To do so, add position: relative; to the div.thumbnail element.
By the script you provided, it seems that you need to place the a#clickMe at the bottom of div.thumbnail.
Now that we are sure that the styles added to a#clickMe is relative to div.thumbnail, just add bottom: 0px; to the a#clickMe element and it will be positioned accordingly, independently of the height that its parent has. Note that this will automatically rearrange when the window is resized (with no script needed).
The final code will be like this (see fiddle here):
JS:
/* No script needed. */
CSS:
div {
width: 200px;
height: 300px;
background-color: purple;
position: relative; //added
}
a {
position: absolute;
bottom: 0px; //added
}
#media (max-width: 991px) {
div {
height: 200px;
}
}
If you still insist on media query change detection, see these links:
http://css-tricks.com/media-query-change-detection-in-javascript-through-css-animations/
http://css-tricks.com/enquire-js-media-query-callbacks-in-javascript/
http://tylergaw.com/articles/reacting-to-media-queries-in-javascript
http://davidwalsh.name/device-state-detection-css-media-queries-javascript
Twitter Bootstrap - how to detect when media queries starts
Bootstrap: Responsitive design - execute JS when window is resized from 980px to 979px
I like your temporary solution (I did that for a similar problem before, I don't think half a second is too long for a user to wait but perhaps it is for your needs...).
Here's an alternative that you most likely have thought of but I don't see it mentioned so here it is. Why not do it all through javascript and remove your #media (max-width.... from your css?
function resize() {
var width = (window.innerWidth > 0) ? window.innerWidth : screen.width;
if(width<992){
$("div").each(function(e,obj){$(obj).height(200);});
}
$('#clickMe').offset({
top: $parent.offset().top + $parent.height()-$('#clickMe').height()
});
}
In the html page, put the link to css file in head section; next, put the link to js file just before the /body tag and see what happens. In this way css will load always before js.
Hope this help you.
Did you try to bind the resize handler not to the window but to the object you want to listen to the resize ?
Instead of
$(window).on('resize', resize);
You can try
$("#clickMe").on('resize', resize);
Or maybe
$("#clickMe").parent().on('resize', resize);
var didResize = false;
$(window).resize(function() {
didResize = true;
});
setInterval(function() {
if (didResize) {
didResize = false;
console.log('resize');
}
}, 250);
I agree with falsarella on that you should try to use only CSS to do what you are trying to do.
Anyway, if you want to do something with JS after the CSS is applied, I think you can use requestAnimationFrame, but I couldn't test it myself because I wasn't able to reproduce the behavior you explain.
From the MDN doc:
The window.requestAnimationFrame() method tells the browser that you
wish to perform an animation and requests that the browser call a
specified function to update an animation before the next repaint. The
method takes as an argument a callback to be invoked before the
repaint.
I would try something like this:
var $parent = $('#clickMe').parent();
function resize(){
$('#clickMe').offset({
top: $parent.offset().top + $parent.height()-$('#clickMe').height()
});
}
window.onresize = function(e){
window.requestAnimationFrame(resize);
}
window.requestAnimationFrame(resize);
Anyone know of a technique to wait till css is completely done loading?
what about $(window).load(function() { /* ... */ } ?
(it executes the function only when the page is fully loaded, so after css loaded)
I'm using PhoneGap and jQuery Mobile in my app. my problem is while I navigating from page A to the page B by one click everything is OK, but when I clicking double click on page A
and passing to next screen (page B) that isnt visable to the user at that second... the second click is passed to the page B and page B try to do the action that was pressed in page A.
Any ideas how to disable any clicks on page B and activate it only after event or page loads for 100%?
Not specific to jQuery Mobile, but you can throw up a "click prevention" DIV to intercept any events you would rather not be handled.
Create a DIV with the following styles:
position: absolute;
top: 0; left: 0; right: 0; bottom: 0;
width: 100%; height: 100%;
background-color: transparent;
z-index: 999999;
transform: translateZ(999999px);
display: none;
Then when you need to prevent any interaction with the app, change that div's style from display:none to display:block. Voila, instant click prevention.
Of course, don't forget to remove it from the DOM or switch it back to display:none -- otherwise your user won't be able to interact with the app anymore.
Alternatively, if you can prevent the browser's default when processing the event, that works out pretty well too. Not sure how jQuery Mobile would do that, but it's easy on something like Hammer.js ( Hammer(element, {prevent_default: true}.on("tap", event_handler); ) If possible, this is the way I'd go, since it avoids touching the DOM (which might trigger reflow). But if you can't get it working any other way, the first method should work, even if a bit ugly.
Consider this page: http://www.collegeanswerz.com/adelphi-university/academics/professors/do-professors-explain-things-clearly-are-professors-interesting.
The element in question is "Do they make things easy to understand? Are they interesting?" in the light gray box on the top right. When the page loads, it starts off high up, and then it moves 30px down. The same thing happens when you click "Information" in the navbar.
This is the element: <div id="question_sub" class="well"></div>.
Why does this happen, and how can I fix it?
Answer to Why does it Happen
If you try loading your page without javascript the page looks like
Problem
Your page is very heavily dependent on js for dom elements modification and for styling also.
Solution To avoid this style your page in css as maximum as possible, JS should be used for interaction or making web page attractive.
Probable Problem
If you are loading lots of external script which are not related to page content like discus inside head element
Solution
Move all the external js from head to end of body if you are not doing it, or you can load them asynchronously. Refer Mozilla Synch and Async
Another Way
If you want content to be loaded from server only when some portion of it has changed then use application cache technique with this the pages will be loaded from client machine so only initial page load will take time for the first load and then it will be quite fast
Check Using Application Cache
Other Ways
Compress Javascript and CSS
Use gzip compression
there are lot of more stuff, search it you will find ocean of knowledge, reference
If you want to keep the 50px margin between the elements then change the navbar class to also be 50px
.navbar {
margin-bottom: 50px;
}
Currently it is set at 20px;
Remove this code :-
comments powered by <span class="logo-disqus">Disqus</span>
This is a problem about fusion-margin
Remove this:
#college_pages_css .questions {
margin-top: 30px;
And try this, it will work fine:
#college_pages_css .questions {
margin-top: 0;
If you want a margin, put the margin on div#normal ;)
It looks like you're having a CSS issue due to the floating elements.
try floating the nav on the left:
#normal > nav {
float: left;
}
.disqus { float: right }
and wrap the following elements in a div that is floated to the right, for exemple:
<div class="disqus">
<div id="question_sub" class="well">Do they make things easy to understand? Are they interesting?</div>
<p class="stratify" style="display: block;">tip: talk about the best/worst/average cases</p>
<div id="disqus_thread">
</div>
This question already has answers here:
Why does jQuery or a DOM method such as getElementById not find the element?
(6 answers)
Closed 9 years ago.
I have very simple code
html
<div id="ball" class="ball"></div>
css
#ball{
width: 20px;
height: 20px;
border-radius: 100%;
background: #0f0;
position: absolute;
bottom: 150px;
left: 350px;
}
javascript
<script type="text/javascript">
document.getElementById('ball').style.backgroundColor="red";
</script>
I tried this code in jsfiddle and it works but why this is not working locally? I tried changing to , but I've no idea why this is not working. It's showing the error:
TypeError: document.getElementById(...) is null
As mentioned in the comment, your initialization order is messed up. You can use window.onload to fix it:
<script type="text/javascript">
window.onload = function() {
document.getElementById('ball').style.backgroundColor="red";
};
</script>
Note also that you can only have one onload trigger function. Here are some ideas on how to support multiple trigger functions. The easiest, is of course, to just use JQuery's ready function.
Another way is to put the <script> tag into the body after the DOM element(s) that it depends on. This is often encouraged for performance reasons, but it tends to make things less readable.
The reason as to why <script> tags in the head are executed in sequence (instead of delaying execution until after the DOM has loaded) is: Performance. For example, you sometimes might want to start asynchronous requests before the document has finished loading. If you are not concerned about performance, it's safer to execute them "onload".
Ultimately, there are a lot of considerations to be made when placing your <script> tag. If you want to learn more, this might be a good starting point.
About the second part of your question: The reason as to why it works in JSFiddle is that, by default, it executes scripts onload. You can reproduce the bug on JSfiddle by choosing "no wrap - in head": http://jsfiddle.net/aDuwg/.