Develop Reference

Issue calculating table scrollbar location

So I have a script that adds a slight shadow to table edge where you can scroll, depending on the location of the scrollbar, but it sometimes doesn't work.
This is one part of it:
$('table').on('scrollstart scrollstop', function(){
if($(this).parent().hasClass('table-wrap')){
var elem = $(this),
elemBody = elem.find('tbody'),
elemParent = elem.parent('.table-wrap');
var scrolled = (elemBody.outerWidth() - elemParent.outerWidth() - elem.scrollLeft());
if(scrolled === 0){
elemParent.addClass('left_active');
elemParent.removeClass('right_active');
} else if(elem.scrollLeft() === 0) {
elemParent.removeClass('left_active');
elemParent.addClass('right_active');
} else {
elemParent.addClass('left_active');
elemParent.addClass('right_active');
}
}
});
This part sometimes I have to add "+1" to "elem.scrollLeft() --here---); to make it work.
var scrolled = (elemBody.outerWidth() - elemParent.outerWidth() -
elem.scrollLeft());
But then I noticed, some tables it helps and on others, it stops working. Meaning when I scroll to right the 'right_active' class will not disappear.
Any suggestions?

Have you tried including scrollbar width in your calculation for var scrolled?
var scrolled = (elemBody.outerWidth() - elemParent.outerWidth() - elem.scrollLeft());
I think you are on the right track but the width is probably not precise since .outerWidth() doesn't include scrollbar width. Hence, the maximum scroll width is always greater than the actual element width.

scroll to a div when scrolling, and scroll to top when div disappear

I have 2 divs on my webpage. first div is "#pattern" (red one), and second on is "#projets".(blue one)
when use scrolls for the first time, the window scrolls automaticaly to the the second div "#projets". I'm using jquery scroll-To plugin.
it works nice, even if when the users scroll with a large amount of scroll there could be on offset from the "#projets" div... If someone has an idea to correct this would be nice, but that's not my main trouble...
Now i'm trying to scroll back to the top of the page ("#pattern" div) as soon as "#pattern" div reappears when scrolling, the red one. so basically it should be as soon as the offset from the top of my screen of my div "#projets" is supperior to 1.
I've tried so many solutions without results, using flags, multiple conditions... it can be the same kind of thing as on this page, but user should be abble to scroll freely inside the page, not scrolling from hash to hash :
http://www.thepetedesign.com/demos/onepage_scroll_demo.html
here is my html :
<div id="pattern"></div>
<div id="projets"></div>
my css :
#pattern {
height:300px;
width: 100%;
background-color:red
}
#projets {
height:800px;
width: 100%;
background-color:blue
}
and my jquery :
var flag=0 ;
$(window).on('scroll',function(){
var top_projets_position = $("#projets").offset().top - $(window).scrollTop();
if((flag==0) && $(window).scrollTop()>1){
$(window).scrollTo('#projets', 500);
flag=1;
}
if($(window).scrollTop()==0){
flag=0;
}
});
here is jsfiddle :
http://jsfiddle.net/jdf9q0sv/
hope someone can help me with this, I can't figure out what I'm doing wrong, maybe a wrong method ! thanks

It looks like you need to track 3 things:
The scroll direction occurs.
The area you are currently viewing.
If scroll animation is currently happening (we need to wait until it's done, or problems will occur).
http://jsfiddle.net/vx69t5Lt/
var prev_scroll = 0; // <-- to determine direction of scrolling
var current_view ="#pattern"; // <-- to determine what element we are viewing
var allowed = true; // <-- to prevent scrolling confusion during animation
var top_projets_position = $("#projets").offset().top + 1;
$(window).on('scroll',function(){
var current_scroll = $(window).scrollTop();
if(current_scroll < top_projets_position && current_view=="#projets" && current_scroll < prev_scroll){
scrollToTarget("#pattern");
}
if($(window).height() + current_scroll > top_projets_position && current_view=="#pattern" && current_scroll > prev_scroll){
scrollToTarget("#projets");
}
prev_scroll = current_scroll;
});
function scrollToTarget(selector){
if(allowed){
allowed = false;
$(window).scrollTo(selector, {
'duration':500,
'onAfter': function(){ allowed = true; current_view = selector;}
});
}
}
This is just a quick solution based on your original code. A better solution would be to do something more Object Oriented (OOP) and track values in an object. Perhaps take an array of elements on object creation, grab all the boundaries and use the boundaries in your scroll handler to determine when to scroll to the next div.

How might I tell if an HTML element is being rendered on the screen?

I'd like an element to do a CSS3 animation once the page is scrolled down enough for it to be visible, and I'm wondering if there's any way to accomplish this. Anything involving JavaScript or CSS would work. I've done many Google searches and Stackoverflow searches and can't find exactly what I need.

Depending on the complexity of your layout, it could be as simple as finding the scroll position, the height of the window, and where the element is on the page.
function scrollEvent() {
var el = document.getElementsByTagName('a')[0];
var body = document.getElementsByTagName('body')[0];
var posY = (window.innerHeight + body.scrollTop) - el.offsetTop;
var onScreen = (posY > 0 && posY < window.innerHeight) ? true : false;
}
window.onscroll = scrollEvent;
Use the same technique if you're worried about horizontal positioning, as well.

It depends on what you want to do specifically. I would look at these resources:
http://daneden.github.io/animate.css/
http://www.w3schools.com/css/css3_animations.asp
http://css-tricks.com/almanac/properties/a/animation/

Put your CSS3 animation style in a class, but don't assign it to your element until it has been scrolled completely into view.
Assuming your element has an id of sprite, this should get you going:
<style>
.animate {
//CSS3 animation style
}
</style>
window.onscroll= function() {
var sprite = document.getElementById('sprite');
if(sprite.getBoundingClientRect().top>=0 && sprite.getBoundingClientRect().bottom<=window.innerHeight) {
sprite.className= 'animate';
}
}

Making nav bar effects using scroll AND click in jQuery

I want a nav to highlight (or something similar) once a user clicks on it AND when a user scrolls to the corresponding section.
However, on my computer when one clicks on any of the nav events after3, only nav event 3 changes. I'm guessing this is because after one clicks on 4 or 5, the scroll bar is already at the bottom of the page, so 4 and 5 never reach the top. The only div at the top is post 3, so my code highlights nav event 3 and ignores the click.
Is there any way I can fix this? Ive tried if statements (only highlight nav event if it's at the top AND the scrollbar isn't at the bottom or the top isn't the last item).
Here is a more accurate fiddle, using a fix below showing what I am talking about. The fix now highlights on scroll, but if you click option 5, it will not highlight.
$('.option').children('a').click(function() {
$('.option').css('background-color', '#CCCCCC;');
$(this).css('background-color', 'red');
var postId = $($(this).attr('href'));
var postLocation = postId.offset().top;
$(window).scrollTop(postLocation);
});
$(window).scroll(function() {
var scrollBar = $(this).scrollTop();
var allPosts = [];
var post = $('.content').offset();
var lastPost = allPosts.legnth-1
var windowHeight = $(window).height();
var bottomScroll = windowHeight-scrollBar;
$(".content").each(function(){
allPosts.push($(this).attr('id'));
});
i = 0;
for(i in allPosts){
var currentPost = "#"+allPosts[i];
var postPosition = $(currentPost).offset().top;
if (scrollBar >= postPosition){
$('.option').css('background-color', '#CCCCCC');
$('#nav'+allPosts[i]).css('background-color', 'red');
};
};
});

I think you've overdone your scroll() handler, to keep it simple you just needs to check if the scrollbar/scrollTop reaches the '.contents' offset top value but should not be greater than its offset().top plus its height().
$(window).scroll(function () {
var scrollBar = $(this).scrollTop();
$(".content").each(function (index) {
var elTop = $(this).offset().top;
var elHeight = $(this).height();
if (scrollBar >= elTop - 5 && scrollBar < elTop + elHeight) {
/* $(this) '.content' is the active on the vewport,
get its index to target the corresponding navigation '.option',
like this - $('.Nav li').eq(index)
*/
}
});
});
And you actually don't need to set $(window).scrollTop(postLocation); because of the default <a> tag anchoring on click, you can omit that one and it will work fine. However if you are looking to animate you need first to prevent this default behavior:
$('.option').children('a').click(function (e) {
e.preventDefault();
var postId = $($(this).attr('href'));
var postLocation = postId.offset().top;
$('html, body').animate({scrollTop:postLocation},'slow');
});
See the demo.

What you are trying to implement from scratch, although commendable, has already been done by the nice folks at Bootstrap. It is called a Scrollspy and all you need to do to implement it is include Bootstrap js and css (you also need jquery but you already have that) and make some minor changes to your html.
Scrollspy implementation steps.
And here is a demonstration. Notice only one line of js. :D
$('body').scrollspy({ target: '.navbar-example' });

Getting Coordinates of an element on page scroll

I am having this problem where i have a set of 6 UL's having a common class x.Each of them consist of a specific section of the page.Now i have 6 menus that are related to each of the section.What i have to do is highlight the menu when its related section is in users view.
For this i thought that may be jQuery position(); or offset(); could have helped but they give the top and left of the element.I also tried using jQuery viewport plugin but apparently view port is big it can show more than one UL at a time hence i cant apply element specific logic here.I am not familliar to this but does anything changes of an element on scrolling?If yes then how to access it?
Please share your views.
Regards
Himanshu Sharma.

Is very easy to do it using jQuery and a dummy fixed HTML block that helps you find the current position of the viewport.
$(window).on("scroll load",function(){
var once = true;
$(".title").each(function(ele, index){
if($(this).offset().top > $("#viewport_helper").offset().top && once){
var index = $(this).index(".title");
$(".current").removeClass('current')
$("#menu li").eq(index).addClass('current')
once = false;
}
});
})
Check out a working example: http://jsfiddle.net/6c8Az/1/
You could also do something similar with the jQuery plugin, together with the :first selector:
$(window).on("scroll load",function(){
$(".title:in-viewport:first").each(function(){
var index = $(this).index(".title");
$(".current").removeClass('current')
$("#menu li").eq(index).addClass('current')
});
})

You can get the viewport's width and height via $(document).width() and $(document).height()
You can get how many pixels user scrolls via $(document).scrollTop() and $(document).scrollLeft
Combining 1 and 2, you can calculate where the viewport rectangle is
You can get the rectangle of an element using $(element).offset(), $(element).width() and $(element).height()
So the only thing left to you is to determine whether the viewport's rectangle contains (or interacts) the elements's rectangle
So the whole code may look like:
/**
* Check wether outer contains inner
* You can change this logic to matches what you need
*/
function rectContains(outer, inner) {
return outer.top <= inner.top &&
outer.bottom >= inner.bottom &&
outer.left <= inner.left &&
outer.right >= inner.right;
}
/**
* Use this function to find the menu related to <ul> element
*/
function findRelatedMenu(element) {
return $('#menu-' + element.attr('id'));
}
function whenScroll() {
var doc = $(document);
var elem = $(element);
var viewportRect = {
top: doc.scrollTop(),
left: doc.scrollLeft(),
width: doc.width(),
height: doc.height()
};
viewportRect.bottom = viewportRect.top + viewportRect.height;
viewportRect.right = viewportRect.left + viewportRect.width;
var elements = $('ul.your-class');
for (var i = 0; i < elements.length; i++) {
var elem = $(elements[i]);
var elementRect = {
top: elem.offset().top,
left: elem.offset().left,
width: elem.width(),
height: elem.height()
};
elementRect.bottom = elementRect.top + elementRect.height;
elementRect.right = elementRect.left + elementRect.width;
if (rectContains(viewportRect, elementRect)) {
findRelatedMenu(elem).addClass('highlight');
}
}
}
$(window).on('scroll', whenScroll);

Let's see if i understood well. You have a page long enough to scroll, and there is an element that when it appears in the viewport, you wanna do something with it. So the only event that's is triggered for sure on the time the element gets in the viewport is the 'scroll'. So if the element is on the page and the scroll is on the viewport, what you need to do is bind an action to the scroll event to check if the element is in the view each time the event is trigger. Pretty much like this:
$(window).scroll(function() {
check_element_position();
});
Now, in order for you to know if the element is in the viewport, you need 3 things. The offset top of that element, the size of the viewport and the scroll top of the window. Should pretty much look like this:
function check_element_position() {
var win = $(window);
var window_height = win.height();
var element = $(your_element);
var elem_offset_top = element.offset().top;
var elem_height = element.height();
var win_scroll = win.scrollTop();
var pseudo_offset = (elem_offset_top - win_scroll);
if (pseudo_offset < window_height && pseudo_offset >= 0) {
// element in view
}
else {
// elem not in view
}
}
Here, (elem_offset_top - win_scroll) represent the element position if there was no scroll. Like this, you just have to check if the element offset top is higher then the window viewport to see if it's in view or not.
Finally, you could be more precise on you calculations by adding the element height (variable already in there) because the code i just did will fire the event even if the element is visible by only 1 pixels.
Note: I just did that in five minutes so you might have to fix some of this, but this gives you a pretty darn good idea of what's going on ;)
Feel free to comment and ask questions