Get percentage of scroll position [duplicate] - javascript

This question already has answers here:
Cross-Browser Method to Determine Vertical Scroll Percentage in Javascript
(14 answers)
Closed 2 years ago.
The problem:
What would be the mathematical formula to calculate (regardless of the
scrollHeight of the document) how far the bottom of the scrollbar is from it's total bottom (which would be the end of the page). So, for example, when the scrollbar is at the top, I would say the distance in percentages of the bottom of it, from the bottom of the document, would be 0%, and when it's totally scrolled all the way (vertically), it would be 100%.
My goal:
My goal is to calculate how many pixels there are between the bottom and a specific position which is, let's say 3%, relative to the viewport, above that bottom. Again, the document height should mean nothing. 3% are 3% if it's relative to the viewport.
Known variables:
var P = 3 // in %
var totalHeight = document.documentElement.scrollHeight;
var viewportHeight = document.documentElement.clientHeight;

Returns a number between 0 to 100 relative to scroll position:
document.onscroll = function(){
var pos = getVerticalScrollPercentage(document.body)
document.body.innerHTML = "<span>" + Math.round(pos) + "%<span>"
}
function getVerticalScrollPercentage( elm ){
var p = elm.parentNode
return (elm.scrollTop || p.scrollTop) / (p.scrollHeight - p.clientHeight ) * 100
}
body{ height:2000px }
span{ position:fixed; font:5em Arial; color:salmon; }
● Difference between scrollHeight & clientHeight

When you scroll to the bottom, the final position value is equal to the height of your document minus the height of one screen (viewport). So if you compute:
scrollPositionRelative = scrollPosition / (documentHeight - viewportHeight);
The values will be in the range 0-1 as expected.
Here's the function used in the example given at the end.
function getScrollPosition () {
var viewportHeight = Math.max(document.documentElement.clientHeight, window.innerHeight || 0); // Viewport height (px)
var scrollPosition = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop; // Current scroll position (px)
var documentHeight = $(document).height(); // Document height (px)
var scrollPositionRelative = scrollPosition / (documentHeight - viewportHeight); // The document height is reduced by the height of the viewport so that we reach 100% at the bottom
return {
documentHeight: documentHeight,
relative: scrollPositionRelative,
absolute: scrollPositionRelative * documentHeight // Yields an "average" pixel position
};
}
See it in action: http://jsbin.com/tawana/1/

Related

If bottom of div is visible jquery

Please help me out here, if bottom of div or full div is visible then i want to scroll to down of next div. Here the code i have tried out,
Mathematically,
var top = $("#myDiv").offset().top;
//top = 1863
var divHeight = $("#myDiv").height();
//divHeight = 571
var total = top + divHeight;
//total = 2434
if($('#myDiv').css('height',total).visible(true))
{
alert('hi');
// I need to alert only if the full div is visible not some part of div
}
else
{
//if height of myDiv is larger window height (my screen height 640 pixels)
}
If all this part of html(from top to divHeight) or bottom of page(here total value) is visible then i need to scroll to next div.
Please note :- the code inside if conditional statement is not correct, i think you got some idea from that.
Given element the jQuery object you want to check, element is fully visible if it is shown and all of the 4 sides of its layout box fall within the window viewport.
Caution: the following solution assumes that there are no element with scrollable overflow between element and the document root, otherwise the calculation becomes way more complicated.
function isFullyVisible(element) {
var offset = element.offset();
var scrollTop = $(document).scrollTop();
var scrollLeft = $(document).scrollLeft();
return element.is(":visible") && // shown
offset.top >= scrollTop && // top
offset.left >= scrollLeft && // left
offset.top + element.outerHeight() <= scrollTop + $(window).height() && // bottom
offset.left + element.outerWidth() <= scrollLeft + $(window).width(); // right
}
If you don't care of sides, you can keep only the corresponding sub-expression.

Interpolating element as it scrolls through window

I'm trying to interpolate a percentage as an element moves through the window as you scroll.
Basically, when the top of the element meets the bottom of the window, that returns 0%. When the bottom of the element meets the top of the window, that returns 100%.
So far I can interpolate using the middle of the element, but I can't figure out how to get it to start at the top and bottom instead of the middle.
Heres a Demo
$(document).ready(()=>{
//Element Vars - Test for Element 3
const $interpolateTarget = $('#element3');
const elementH = $interpolateTarget.height();
const elementY = $interpolateTarget.offset().top;
//Window Vars
const windowH = $(window).height()
let scrollY;
let interpolation;
let middlePoint;
$(window).scroll((event)=>{
scrollY = $(window).scrollTop()
pctOfWindow = elementH / windowH
//Calculate middle of element and compare to middle of window
middleY = elementH / 2 + elementY - scrollY
windowMiddleY = windowH / 2
interpolation = middleY / windowMiddleY / 2
//Convert to percentage and reverse
interpolation = (interpolation * 100 - 100 ) * -1
updateInfo(scrollY, interpolation);
})
})
Any Help would be greatly appreciated, thanks!
I think you need to consider the document height instead of the window height. The following may help you.
updateInfo(scrollY, 100 * $(document).scrollTop() / ($(document).height() - $(window).height()));
$(document).scrollTop() : how much is scrolled in the entire document
$(document).height() : actual document height
$(document).height() - $(window).height() : scrollable document height
Seems I figured it out, changed elementH / 2 + elementY - scrollY to elementH + elementY - scrollY

Why is my jQuery resize firing inconsistently?

I'm wrapping up a site that involves a few elements (image / text / diagonal line) that have to scale proportionately on different screens.
Because there's text that has to be resized, I'm using jQuery to calculate the measurements for all of the elements based on a ratio. This was the best solution I could think of at the time, and with a deadline approaching, I think I'm stuck with it. It's a single-page site that scrolls by the page (e.g., full pages in the viewport).
Here's a link to the demo site
The idea behind the code:
We check the height of the viewport to set the container size
Set the wrapper element height, based on the container size and necessary
margins
Set the width based on a ratio
Use these values to calculate font size, image size, and offsets
As the screen is re-sized, the element shrinks proportionately to fill the available space.
It looks kind of like this:
There are two panels like this. I re-use the same code (with different variable names, and a few sizing differences) for the second panel.
Here's my Javascript/jQuery for the first:
// Set panel height on page load & resize
$(window).on("resize", function () {
var $panelHeight = $(window).height();
var $headerHeight = $('.banner').height();
// General height for panels
$('.bg-panel').css('height', $panelHeight );
$('.bg-panel').css('padding-top', $headerHeight);
}).resize();
// We want to scale content proportionately
// First let's get some breakpoints
var $breakPoint = 768;
var $breakPointSM = 480;
// Panel 1
$(window).on("resize", function () {
// Check height of current panel
// If on single-column view, we want to measure the space between the text column and bottom of screen
// Otherwise, height of entire panel
var $windowHeight = $('.panel-test').height();
// But we need to subtract the header height, so our math is correct
var $headerHeight = $('.banner').height();
var $windowHeight = $windowHeight - $headerHeight;
// Now we have the correct height to work with
// We're at 768px or below, subtract the text element from the overall height
if ( $(document).width() <= $breakPoint) {
var $heightofDiv = $('.panel-1-text').height();
var $mobileHeight = $windowHeight - $heightofDiv;
var $windowHeight = $mobileHeight;
}
// Save the window height for calculating our margins!
var $windowHeightforMargins = $windowHeight;
// Top and bottom margins
var $marginTop = $windowHeight * (102/792); // ratio from PSD
var $marginBottom = $windowHeight * (84/792); // ratio from PSD
var $marginTotal = $marginTop + $marginBottom;
// Responsive solution
// As browser shrinks, reduce the height of panel so it produces a smaller container
if ( $(document).width() > 1200 && $(document).width() <= 1440) {
var $windowHeight = $windowHeight * 0.9;
var $marginTop = $marginTop * 2;
}
else if ( $(document).width() > 990 && $(document).width() <= 1200) {
var $windowHeight = $windowHeight * 0.8;
var $marginTop = $marginTop * 3;
}
else if ( $(document).width() > $breakPoint && $(document).width() <= 990) {
var $windowHeight = $windowHeight * 0.7;
var $marginTop = $marginTop * 3.5;
}
else if ( $(document).width() < $breakPoint) { // Ratio here goes up again because we're accounting for new height with $mobileHeight
var $windowHeight = $windowHeight * 0.8;
}
// This ratio determines the width of the container
var $ratio = 697 / 607; // from PSD
// Set container height, depending on height of panel
if ( $(document).width() <= $breakPointSM) {
var $taglinesHeight = ($windowHeight * 1.5); // Scale up for phones
}
else if ( $(document).width() > $breakPointSM && $(document).width() <= $breakPoint ){
var $taglinesHeight = ($windowHeight * 1); // Scale down for tablet
}
else {
var $taglinesHeight = $windowHeight - $marginTotal;
}
// Set container width as ratio of height
if ( $(document).width() <= $breakPoint) {
var $taglinesWidth = $taglinesHeight * $ratio
} else {
var $taglinesWidth = $taglinesHeight * $ratio
}
$('.panel-test .bg-taglines').css("width", $taglinesWidth);
$('.panel-test .bg-taglines').css("height", $taglinesHeight);
// Add top margin if above breakpoint
if ( $(document).width() > $breakPoint) { // No margin unless above 768px
$('.panel-test .bg-taglines').css("margin-top", $marginTop);
}
else {
$('.panel-test .panel-1-tagline').css("bottom", $marginTop);
}
// Set font size
var $fontSize = $taglinesWidth * 0.12;
$('.bg-panel h4').css("font-size", $fontSize);
// Set pink line origin (relative to bottom-left of frame)
var $pinkX = $taglinesWidth * (286 / 705);
var $pinkY = $taglinesHeight * (192 / 607);
$('.panel-test .animation-wrapper').css("left", $pinkX);
$('.panel-test .animation-wrapper').css("bottom", $pinkY);
// Set image size
var $imageWidth = $taglinesWidth * 0.556;
$('.panel-test .scaleable-image').css("width", $imageWidth);
// Set h3 margin from top
if ( $(document).width() >= $breakPoint) {
var $marginH3 = $windowHeight * (217/792); // ratio from PSD
$('.panel-test h3').css("margin-top", $marginH3);
} else {
// CSS
}
// Set line offset from top
var $lineOffset = $taglinesHeight * 0.7;
$('.panel-test .line-wrapper').css("top", $lineOffset);
// Set line length
var $lineLong = $taglinesWidth * 1;
$('.panel-test .pink-line').css("width", $lineLong);
}).resize();
It works: MOST of the time.
If I drag my window to resize, some of the elements get resized. Others don't.
A page refresh generally solves it, but right now, elements (mostly the images!) just aren't scaling properly and in sync with other elements.
I'm very new to jQuery and this is my first big undertaking. New to using resize as well. Hoping I just made a goof that's easy to fix.
Thanks!
LIVE SITE LINK
Other plugins in use: jQuery Scrollify (for full page scrolling) and ScrollReveal.
Guess I can answer my own question.
The issue seemed to be that the values were getting mixed up when scrolling from one full-screen panel to another.
Changing this:
$(window).on("resize", function () {
To this:
$(window).on("resize load scroll", function (e) {
... solved the issue. I'm not sure if it's the right way to do it, but the resizes are all working fine now.

Why is the document height equal to window inner height + pageYoffset?

I am trying to detect when an user has scroll to the very bottom of the page.
The solution that I end up with is the following
var windowHeight = "innerHeight" in window ? window.innerHeight : document.documentElement.offsetHeight;
var body = document.body, html = document.documentElement;
var docHeight = Math.max(body.scrollHeight, body.offsetHeight, html.clientHeight, html.scrollHeight, html.offsetHeight);
var windowBottom = windowHeight + window.pageYOffset;
if (windowBottom >= docHeight) {
// Bottom is reached
}
I am confused why this works
From the documentation, innerheight is the height of the view portal, and pageYoffset is the amount of scroll that we make.
So in order to detect scroll to bottom, shouldn't I check if pageYOffset >= documentHeight ?
Why do I have to add innerheight?
This has nothing to do with Angular. This is how all browsers work.
Your pageYOffset is never going to be greater than the document height since it represents the top of the viewport. In order for pageYOffset to be equal to the document height, you'd have to scroll past the end of the page.
The maximum pageYOffset can be is the docHeight - window.innerHeight. So your check could be:
if (pageYOffset >= docHeight - window.innerHeight) {
// Bottom is reached
}

How to shrink an image width based on scroll position

I'm looking to shrink a logo based on scroll
So far, I have something like this
logoSize = function(){
var headerOffset = $(window).height() - 650;
var maxScrollDistance = 1300;
$(window).scroll(function() {
var percentage = maxScrollDistance / $(document).scrollTop();
if (percentage <= headerOffset) {
$('.logo').css('width', percentage * 64);
}
console.log(percentage);
});
}
logoSize();
I'm close, but the image either starts too wide or it shrinks too quickly, I need it to happen for the first 650px of scroll as you can see - Any ideas? Perhaps a percentage width would be better?
I've re-written your code based on the assumption that you have a target size in mind , e.g. after scrolling 650px you want your image to be 250px wide.
It scrolls smoothly between the native size and the target size, and takes into account the fact that the window height could be less than your maximum scrolling distance:
logoSize = function () {
// Get the real width of the logo image
var theLogo = $("#thelogo");
var newImage = new Image();
newImage.src = theLogo.attr("src");
var imgWidth = newImage.width;
// distance over which zoom effect takes place
var maxScrollDistance = 650;
// set to window height if that is smaller
maxScrollDistance = Math.min(maxScrollDistance, $(window).height());
// width at maximum zoom out (i.e. when window has scrolled maxScrollDistance)
var widthAtMax = 500;
// calculate diff and how many pixels to zoom per pixel scrolled
var widthDiff = imgWidth - widthAtMax;
var pixelsPerScroll =(widthDiff / maxScrollDistance);
$(window).scroll(function () {
// the currently scrolled-to position - max-out at maxScrollDistance
var scrollTopPos = Math.min($(document).scrollTop(), maxScrollDistance);
// how many pixels to adjust by
var scrollChangePx = Math.floor(scrollTopPos * pixelsPerScroll);
// calculate the new width
var zoomedWidth = imgWidth - scrollChangePx;
// set the width
$('.logo').css('width', zoomedWidth);
});
}
logoSize();
See http://jsfiddle.net/raad/woun56vk/ for a working example.

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