Trigger JQuery function when passed half way down the page - javascript

Is there a way to tell if you have scrolled passed the center of the web page or in other words, when you have scrolled passed exactly half of the web page and your scrollbar is situated in the lower half of the browser window?
I want to be able to trigger this:
$('.pineapple-man').show(); when I have scrolled down passed half of the page?
Is this possible at all?
Your help would be so kind!

You can get the pixel amount of an element has been scrolled by using .scrollTop(). To listen to scroll events use .scroll().
When you want to identify the halfway, use height of the scroll:
$(window).scroll(function () {
if ($(window).scrollTop() > $('body').height() / 2) {
$('.pineapple-man').show();
}
});
If you are scrolling some other element than the whole window/body, please feel free to change the selectors.
To make the showing one-timer, add the removal of scroll event listener, by adding the following after the .show() call:
$(window).unbind('scroll');

I guess you want to do something like this:
if($(document).scrollTop() > $(document).height()/2){
$('.pineapple-man').show();
}
where scrollTop() gets the current horizontal position and height() defines the document height.

See the scroll event and the scrollTop method.

you can use the focus event if you scroll down to it (just like jQuery uses for their comments)
jQuery('selector').focus(function() {
jQuery('.page').show();
});

Related

Detect when the end of a div is visible

I need to know if the end of a div element is currently visible in the users' browser.
I tried something I saw on the web, but scrollTop() always gave me zero in my Browser. I read something about an issue in Chrome, but I didn't understand quite well.
jQuery(
function($) {
$('#flux').bind('scroll', function() {
if ($(this).scrollTop() + $(this).innerHeight() >= $(this)[0].scrollHeight) {
alert('end reached');
}
})
}
);
My idea is the following:
1- User loads page and sees a Bar (sticky div at bottom visible page) with some information.
2- After scrolling a bit, and reaching the end of a div element, this bar will position there, after the div. This is the bar's original position
I wasn't really able to know when I was at the end of the div element. Eventually I found this code:
if ($(window).scrollTop() >= $('#block-homepagegrid').offset().top + $('#block-homepagegrid').outerHeight() - window.innerHeight) {
$('.hero-special-message').removeClass('hero-special-messege-scrolling');
} else {
$('.hero-special-message').addClass('hero-special-messege-scrolling');
}
});
I see that it's working, but I'm having a bit of trouble understanding what it does.
I know the following:
1. $(window).scrollTop();
this gives me the amount of pixels the user has scrolled, pretty self explanatory.
2. $('#block-homepagegrid').offset().top;
I THINK this is the distance between the start of the page and the start of the div. I know it's the current coordinates, but what is top exactly here?
3. $('#block-homepagegrid').outerHeight();
this gives the height of the element, I know there are 3, like
height(), innerHeight() and outerHeight(), if you want to take into
account border, margin, padding, which is the better to use?
4. window.innerHeight;
I understand this is what the user sees, but I'm having troubles understanding why does it matter for my situation.
Thanks!
You may be interested in the native JavaScript IntersectionObserver API. It automatically figures out what percentage of a given element is visible in the window and triggers callbacks based on that. So then you can do this:
function visibleHandler(entries) {
if (entries[0].intersectionRatio >= 1.0) {
// The whole element is visible!
} else {
// Part of it is scrolled offscreen!
}
}
const observer = new IntersectionObserver(visibleHandler, {threshold: 1.0});
observer.observe(document.getElementById('flux'));
Now, whenever the element with ID flux is 100% in view, it will trigger the visibleHandler. It will also trigger again if it's scrolled back out of view; that's why the function checks the ratio of visibility to see if it just hit 100% or just got reduced from 100%. You could be more fancy and use the observer entry's insersectionRect, which gives you the rectangle containing the visible portion of the element, and use that to determine top/bottom visibility.

How do I change this script to use a number to show content using JQuery?

This is my code:
$( document ).ready(function() {
var target = $(".passthis").offset().top-$(window).height();
$(document).scroll(function() {
if ($(window).scrollTop() >= target) {
$(".something").fadeIn(2000);
}
});
});
HTML:
<div class="passthis" style="text-align:center;font-size:20px;margin-top:815px;">
Scroll Below here
</div>
Right now this code will show div.something only when the user passes div.passthis. The .passthis div is exactly at the bottom of the screen. Howver, I want to move .passthis the middle of the screen but being new to JS i am unsure how i can modify my script to do that. Can I use a number for x,y or something?
Question:
What can I do to move the .passthis to the middle of the screen and still make .something show after the user passes .passthis.
Here is a jsFiddle demo that you are welcome to play with. As I explained, if the window never scrolls, nothing is going to happen (.something will never appear). Additionally, you can see the numbers for the different values in this demo. It should give you an idea of what you're shooting for as far as the MATH of it all is concerned. As recommended above, you should read up on jQuery's .scrollTop() and other window dimensional methods and values.

Scroll to an html element with a particular id in javascript or jquery

I have html elements with id's assigned. Now I want to scroll to those elements. I see jQuery has a scrollTop which takes an integer value.. How do I easily just make a particular html element with an id scroll to the top? Ideally, with nice and smooth animation.
A quick search showed many scrolling plugins... if a plugin is needed for the above functionality, what's the most popular one? I'm also using jquery-ui.
You could use something like this to scroll to #someElement when the page loads:
$(document).ready(function() {
$("html, body").animate({scrollTop: $("#someElement").offset().top}, 1000);
});
It simply animates the scrollTop property of the body element, and uses the top offset of some specific element as the position to scroll to. The animation lasts for 1000ms.
Note: it selects both html and body so it works across browsers. I'm not sure on the specifics, but some quick tests show that Chrome uses body, but Firefox and IE use html.
Here's a working example.
Consider the following snippet:
$('#myDiv').bind('click',function(){
var pos = $(this).offset().top,
scrollSpeed = 2;
for (var i = pos; i > 0; i=i-scrollSpeed) {
$(window).scrollTop(i);
}
});
It scrolling was binded to #myDiv element on click just for example. Code determines a position of #myDiv element, than calculates number of scroll steps (speed/smoothness). Than does jQuery .scrollTop() thing.

how to detect document size change in jquery

so suppose that clicking something would lead to a new content being loaded to the screen hence the height of document changes and whereas previously there are no scroll bars, now there actually are scrollbars...
how do I detect something like that happening using jquery
binding resize event onto window only detects window resize whereas binding it into document doesn't work
Update:
Please don't use the DOMSubtreeModified event. It is old, deprecated and not well-supported by browsers. In 99,9 % of the cases, there is a different event you can listen on. Most likely you are one of those people using jQuery and doing some AJAX stuff, so please take a look at their AJAX docs.
These are all available events. You would have to detect $(document).bind('DOMSubtreeModified', function() { ... }); and check for a dimension change to the previous firing.
var height = $(this).height(),
width = $(this).width();
$(document).bind('DOMSubtreeModified', function() {
if($(this).height() != height || $(this).width() != width) {
recalibrate();
}
});
This event is firing every time anything is done to the DOM. Therefore it will slowdown your browser.
We should get a better alternative. Could you please give us more information to your scenario?
Here is the solution.
// ajdust margins when page size changes (ie rotate mobile device)
$(window).resize(function() {
// Do something more useful
console.log('doc height is ' + $(window).height());
});
You could try a percentage scrolled event like this one:
http://www.jquery4u.com/snippets/jquery-detect-scrolled-page/
You might need to add a check to see whether the vertical scrollbar is present:
var hasVScroll = document.body.scrollHeight > document.body.clientHeight;

Scrollbar appear / disappear event in jQuery?

Is there a simple way in jQuery to detect when scrollbars appear and disappear on a div that has overflow:auto? (Like an event? Fingers crossed...)
(I'd prefer not to have to look at the height of the content of the div)
Another way to achieve this is to check whether there are scrollbars present using scrollLeft or scrollTop:
//nudge the scrollbar away from its starting position
$('#your_selector').scrollLeft(1);
//A value of 0 is assigned if the scrollbars are at their default position,
//or are abscent
if($('#your_selector').scrollLeft() !== 0) return true;
//put the scrollbar back to its starting position
$('#your_selector').scrollLeft(0);
As others have said, there is no easy way. Here's some code I've used in the past to detect if a scrollbar is present.
// Used like $('#my-id').hasScrollbar();
jQuery.fn.hasScrollbar = function() {
var scrollHeight = this.get(0).scrollHeight;
//safari's scrollHeight includes padding
if ($.browser.safari)
scrollHeight -= parseInt(this.css('padding-top')) + parseInt(this.css('padding-bottom'));
if (this.height() < scrollHeight)
return true;
else
return false;
}
You'll manually need to call this after adding or removing content from the div and it probably will only work if you call it on visible elements, but it's better than starting from scratch.
As far as I know, there is not event for that.
However, you "could" write your own special event for that, I guess you have to check
for the height and width.
It should be possible to detect scrollbars if the .innerHeight exceds the .outerHeight
value of an element.

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