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How to auto scroll (up&down) to section when user scroll (not click!)

I'm trying to achieve a sliding scroll (like fullPage.js) by myself. I don't want to create a plugin either use a plugin. I only want to scroll/slide to a section when user trigger scroll (up and down!).
I've searched all over the internet and I do not know how to prevent the user from scrolling to replace standard scroll behavior by my animated scroll (desktop and mobile). I want to implement this animation inside a Bootstrap carousel item.
Summarizing, I have a carousel with several items, and each item will have a caption (outside the viewport). When the user scrolls down, then I will show the caption (like third slide here), and when the user scrolls up, I will scroll up and hide the caption.
Here is the CodePen with the carousel example running: link
This is what I get so far (I've got part of the code from StackOverflow)...
$(function(){
var _top = $(window).scrollTop();
var _direction;
$(window).scroll(function(){
var _cur_top = $(window).scrollTop();
if(_top < _cur_top)
{
_direction = 'down';
window.scrollTo(0, document.body.scrollHeight);
} else {
_direction = 'up';
window.scrollTo(0, 0);
}
_top = _cur_top;
console.log(_direction);
});
});
I get a very (very!) slow animation... It is not smooth at all.
I've tried this too:
$(document.body).on('DOMMouseScroll mousewheel', function (event) {
event.preventDefault();
if (event.originalEvent.wheelDelta > 0 || event.originalEvent.detail < 0) {
// Scroll up
$("html, body").animate({scrollTop: 0}, 400);
}
else {
// Scroll down
}
});
But, that code does not work and I get this error: [Intervention] Unable to preventDefault inside passive event listener due to the target being treated as passive.
I will be very thankful if you can help me, please!
Edited:
Someone helped me at "StackOverflow en español". Here is the solution!! Many thanks to #matahombres ;)

Scroll duration when scrolled

I am using Jquery to create an effect that will change things as the user scrolls
$(function() {
var headerPosition = $(".home-header");
$(window)
.scroll(function() {
var scroll = $(window)
.scrollTop();
if (scroll >= 200) {
headerPosition.addClass("home-header-color");
} else if (scroll <= 600) {
headerPosition.removeClass("home-header-color");
}
});
});
This is what i'm using a simple add remove class function that gets triggered on a certain scroll amount.
What I want to do is to make it as a user scrolls once no matter how fast.
This is what I came up with but dose not work well scrolling up.
Codepen
I want it to only appear when you reach the top of the screen when scrolling up. Not on just one scroll up.
I tried combining the two but it didn't work out well.

jQuery: How to detect when user scrolls to the top again?

On the top of my site I have a bar with similar blog posts.
**It should SlideUp (with jQuery) when the user have scrolled to the top again - so e.g. after he read the article.
How can I detect this situation and then show the bar in the head of my site?**

you can monitor scroll event of window element,and check its scrollTop() :
$(window).scroll(function () {
if ($(this).scrollTop() <= 0 ){
// your code
}
});

It's easy to check the scroll position with .scrollTop() in jquery.
So the idea is to bind an event on scroll to check the position periodically.
hasReadArticle = false
$window = $(window)
articleBottomPosition = ... # get the position of the bottom of the article
timeout = nil
$window.on "scroll", (e) ->
clearTimeout timeout if timeout
timeout = setTimeout ->
top = $window.scrollTop()
# you might want to improve this to detect when the bottom of your window arrives at the bottom of the article.
hasReadArticle = top > articleBottomPosition unless hasReadArticle
if top <= 0 && hasReadArticle
# $('your header').slideDown()
, 100
A simpler way to do it would be to use jquery-waypoints. You would set a handler to detect when you get to the bottom of your article, then set a variable to remember this. Then set another handler to detect when you get to the top of the page (with direction == "up").

Floating elements on scroll

I was wondering how sites like Facebook, with their timeline feature, float a certain element (usually a menu bar, or sometimes a social plugin, etc) when the user has scrolled past a point such that the top of the element is off the screen, etc.
This could be seen as a more general JavaScript (jQuery?) event firing when the user has scrolled to a certain element, or scrolled down a certain number of pixels.
Obviously it would require toggling the CSS property from:
#foo { position: relative; }
to
#foo { position: fixed; }
Or with jQuery, something like:
$('#foo').css('position', 'fixed');
Another way I have seen this implemented is with blogs, where a popup will be called when you reach the bottom, or near the bottom of a page. My question is, what is firing that code, and could you link or provide some syntax/ semantics/ examples?
Edit: I'm seeing some great JS variants coming up, but as I am using jQuery, I think the plugin mentioned will do just nicely.

Take a look at this jsfiddle: http://jsfiddle.net/remibreton/RWJhM/2/
In this example, I'm using document.onscroll = function(){ //Scroll event } to detect a scroll event on the document.
I'm then calculating the percentage of the page scrolled based on it's height. (document.body.scrollTop * 100 / (document.body.clientHeight - document.documentElement.clientHeight)).
document.body.scrollTop being the number of pixels scrolled from the top, document.body.clientHeight being the height of the entire document and document.documentElement.clientHeight being the visible portion of the document, a.k.a. the viewport.
Then you can compare this value to a target percentage, an execute JavaScript. if(currentPercentage > targetPercentage)...
Here's the whole thing:
document.onscroll = function(){
var targetPercentage = 80;
var currentPercentage = (document.body.scrollTop * 100 / (document.body.clientHeight - document.documentElement.clientHeight));
console.log(currentPercentage);
if(currentPercentage > targetPercentage){
document.getElementById('pop').style.display = 'block';
// Scrolled more than 80%
} else {
document.getElementById('pop').style.display = 'none';
// Scrolled less than 80%
}
}
​If you prefer jQuery, here is the same example translated into everybody's favorite library: http://jsfiddle.net/remibreton/8NVS6/1/
$(document).on('scroll', function(){
var targetPercentage = 80;
var currentPercentage = $(document).scrollTop() * 100 / ($(document).height() - $(window).height());
if(currentPercentage > targetPercentage){
$('#pop').css({display:'block'});
//Scrolled more than 80%
} else {
$('#pop').css({display:'none'});
//Scrolled less than 80%
}
});​

An idea would be to handle the window.scroll event and determine if the user has scrolled to the bottom of the page. Here is an example:
http://chrissilich.com/blog/load-more-content-as-the-user-reaches-the-bottom-of-your-page-with-jquery/
Hope it helps!

There is a jquery plugin that might help you in the right direction.
http://imakewebthings.com/jquery-waypoints/

I just answered basically the same question here. In that case it was a table and its header, and the basic idea is like this:
function placeHeader(){
var $table = $('#table');
var $header = $('#header');
if ($table.offset().top <= $(window).scrollTop()) {
$header.offset({top: $(window).scrollTop()});
} else {
$header.offset({top: $table.offset().top});
}
}
$(window).scroll(placeHeader);
Here's a demo.
Quoting myself:
In other words, if the top of the table is above the scrollTop, then
position the header at scrollTop, otherwise put it back at the top of
the table. Depending on the contents of the rest of the site, you
might also need to check if you have scrolled all the way past the
table, since then you don't want the header to stay visible.
To answer your question directly, it is triggered by checking the scrollTop against either the position of an element, or the height of the document minus the height of the viewport (for the scrolled to bottom use case). This check is done every time the scroll event is fired (bound using $(window).scroll(...)).

Javascript to detect if item no longer visible due to scrolling

I've got a javascript slideshow at the top of my page. When a slide changes to the next image, I call another function to change the background colour of the page.
The client wants the background colour to stop changing when the slideshow is no longer in view, i.e. when the user has scrolled down the page.
Is there any way to detect if an element is no longer visible due to scrolling?

Test code in jQuery
function test() {
var $elem = $('.test');
var visibleAtTop = $elem.offset().top + $elem.height() >= $(window).scrollTop();
var visibleAtBottom = $elem.offset().top <= $(window).scrollTop() + $(window).height();
if (visibleAtTop && visibleAtBottom) {
alert('visible');
} else {
alert('invisible (at ' + (visibleAtTop ? 'bottom' : 'top') + ')');
}
}
Full working example at http://jsfiddle.net/9PaQc/1/ (Updated: http://jsfiddle.net/9PaQc/2/ )
P.S. This only checks for vertical scroll. For horizontal, just do the same with top replaced with left, Y -> X and height() -> width()
EDIT
Made it all the way jQuery (to ensure x-browser compatibility) by changing window.scrollY -> $(window).scrollTop()

You can use the jQuery $.scrollTop function, probably from a scroll event handler to script this.

Use the window.pageYOffset to determine scroll amount in window. Use current offset of the object to check if it is in view. Note that these values are mostly browser dependent, so first check if it exists then act on it.