Develop Reference

jQuery scrollTop() returns wrong offset on scroll-direction change

I'm trying to get the correct scroll direction via jQuery's "scroll" event.
For this, I'm using the solution here: https://stackoverflow.com/a/4326907/8407840
However, if I change the direction of my scroll, the offset returned by scrollTop is incorrect on the first time. This results in the following behavior:
Wheel down -> down
Wheel down -> down
Wheel up -> down
Wheel up -> up
Wheel down -> up
Wheel down -> down
... and so on, I think you get it.
var ACTIVE_SECTION = null;
var ANIMATION_DURATION = 700;
$(document).ready(function() {
ACTIVE_SECTION = $("section:first-of-type").get(0);
var prevPosition = $(window).scrollTop();
$(window).on("scroll", function() {
doScrollingStuff(prevPosition);
});
});
function doScrollingStuff(prevPosition) {
var ctPosition = $(window).scrollTop();
var nextSection = ACTIVE_SECTION;
// Remove and re-append event, to prevent it from firing too often.
$(window).off("scroll");
setTimeout(function() {
$(window).on("scroll", function() {
doScrollingStuff(prevPosition);
});
}, ANIMATION_DURATION + 100);
// Determine scroll direction and target the next section
if(ctPosition < prevPosition) {
console.log("up");
nextSection = $(ACTIVE_SECTION).prev("section").get(0);
} else if(ctPosition > prevPosition) {
console.log("down");
nextSection = $(ACTIVE_SECTION).next("section").get(0);
}
// If a next section exists: Scroll to it!
if(typeof nextSection != 'undefined') {
var offset = $(nextSection).offset();
$("body, html").animate({
scrollTop: offset.top
}, ANIMATION_DURATION);
ACTIVE_SECTION = nextSection;
} else {
nextSection = ACTIVE_SECTION;
}
console.log(ACTIVE_SECTION);
prevPosition = ctPosition;
}
section {
width:100%;
height:100vh;
padding:60px;
box-sizing:border-box;
}
section:nth-child(1) { background:#13F399; }
section:nth-child(2) { background:#14FD43; }
section:nth-child(3) { background:#4EE61E; }
section:nth-child(4) { background:#BEFD14; }
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<section id="sect1">Section 1</section>
<section id="sect2">Section 2</section>
<section id="sect3">Section 3</section>
<section id="sect4">Section 4</section>
Here's a pen, where you can see my implementation: https://codepen.io/EigenDerArtige/pen/aVEyxd
I am trying to accomplish an autoscroll to the next or previous section, whenever the user scrolls or swipes up/down... Therefore I only fire the "scroll"-event once every second, to prevent multiple scrolljacks all happening at once... However the above behavior seems to result in the user being scrolled to the wrong section.
I've been trying for a couple of hours now to get it working, but to no avail. Help is greatly appreciated!

The problem lies in the assignment prevPosition = ctPosition.
Each time the scroll handler runs, var ctPosition = $(window).scrollTop(); is good for determining scroll direction, however it's not the value that should be rememberad as prevPosition.
prevPosition needs to be $(window).scrollTop() as measured after the animation has completed.
Try this :
$(document).ready(function() {
var ANIMATION_DURATION = 700;
var ACTIVE_SECTION = $("section:first-of-type").eq(0);
var prevPosition = $(window).scrollTop();
$(window).on("scroll", doScrollingStuff);
function doScrollingStuff(e) {
$(window).off("scroll");
var ctPosition = $(window).scrollTop();
var nextSection = (ctPosition < prevPosition) ? ACTIVE_SECTION.prev("section") : (ctPosition > prevPosition) ? ACTIVE_SECTION.next("section") : ACTIVE_SECTION; // Determine scroll direction and target the next section
// If next section exists and is not current section: Scroll to it!
if(nextSection.length > 0 && nextSection !== ACTIVE_SECTION) {
$("body, html").animate({
'scrollTop': nextSection.offset().top
}, ANIMATION_DURATION).promise().then(function() {
// when animation is complete
prevPosition = $(window).scrollTop(); // remember remeasured .scrollTop()
ACTIVE_SECTION = nextSection; // remember active section
$(window).on("scroll", doScrollingStuff); // no need for additional delay after animation
});
} else {
setTimeout(function() {
$(window).on("scroll", doScrollingStuff);
}, 100); // Debounce
}
}
});

js animate function scrolls to bottom of div instead of top

js windows animate scrolltop to div class is scrolling right to to the bottom of the div
js
$(document).ready(function () {
$('html, body').animate({
scrollTop: $('.tariff').offset().top
}, 'slow');
});
it is scrolling right to the bottom of div class 'tariff'. I want it to scroll and stop at the top of the div.
Did a lot of googling. Don't know where I am going wrong.
EDIT
I think it may have something to do with my external js.js file. Something here is probably effecting the animate scrolling height. Because if I omit this file,
it scrolls properly to the top of the div.
But I don't know what is interfering here.
js.js
$('document').ready(function(){
$('#smshare').click(function() {
$('#smp').slideToggle('fast');
$('#smp').load('social-media-share.php');
});
$('#offer,#orderlink').click(function()
{
$('#order').fadeIn('fast');
$('html, body').animate({
scrollTop: $("#order").offset().top
}, 2000);
$('.scrolltop').fadeIn('fast');
$('.aboutus,.tariff,.services,.contactus,.logged_order,.pers_dets,.clothes_submitted,.locations_list').fadeOut('fast');
});
$('.scrolltop').click(function(){
$('#order').fadeOut('fast');
$('html, body').animate({
scrollTop: $(".header").offset().top
}, 2000);
$('.scrolltop').fadeOut('fast');
});
$('#svl').click(function()
{
$('html, body').animate({
scrollTop: $(".service_locations").offset().top
}, 2000);
});
$('.more1').click(function() {
$('.more_dry_cleaning').slideToggle('fast');
$('.more1').fadeOut('fast');
});
$('.less1').click(function() {
$('.more_dry_cleaning').fadeOut('fast');
$('.more1').fadeIn('fast');
});
var valid=0;
$('form[name=orderform]').submit(function(e) {
// alert('Got you!');
$('.clothesqty').each(function(){
// alert('Got you!');
if($(this).val() != 0) {valid+=1;}
});
if(valid!=0){
// e.preventDefault();
// alert(valid + " inputs have been filled");
return true;
}
else {
e.preventDefault();
//alert('Houston we have contact!');
alert("error: you must fill in at least one field");
return false;
}
});
var oblen=Object.keys(item).length;
var zero=0;
var cloth = "";
var i;
var it=1;
var totitems=0;
var tot=0;
var totcost=0;
var itemid="";
var itemclass="";
var totval=0;
for (var key in item) {
if (!item.hasOwnProperty(key)) {
//The current property is not a direct property of p
continue;
}
var k=key;
var v=item[key];
// alert(v);
cloth = k.replace(/ |-|&|\//g, '').toLowerCase();
itemid="#" + cloth;
itemclass="#" + cloth + "cost";
// alert(v+"/"+itemid);
$(itemid).keyup((function (id, cls,itm,val) {
return function () {
var x = $(id).val();
if(x!=0){
itemtot=x * val;
// alert(itm+"->"+itemtot + "=" + x + "x" + val);
$(cls).css("background-color", "#446666").css("padding","3px").css("color","white").css("width","60px").html("Rs." + itemtot);
}else{
$(cls).css("background-color", "#446666").css("padding","3px").css("color","white").css("width","60px").html("Rs." + zero);
}
}
} (itemid, itemclass,cloth,v)));
}
$("input").each(function() {
$(this).keyup(function(){
// calculateCost();
calculateSum();
});
});
});
//Totals
function calculateSum() {
var sum = 0;
var totcost=0;
//iterate through each textboxes and add the values
$("input").each(function() {
//add only if the value is number
if(!isNaN(this.value) && this.value.length!=0 && this.value.length<=3) {
sum += eval(parseInt(this.value));
}
});
$("div.ittot").each(function() {
var tots=0;
var str=$(this).text();
var thenum = str.replace( /^\D+/g, '');
var tots = parseInt(thenum,10);
//add only if the value is number
//if(!isNaN(tots) && tots.length!=0) {
totcost += tots;
//}
});
// alert(totcost);
$("#totalcost").css("background-color", "green").html("<div style='float:left;margin-left:5px'><span style='font-weight:700'>Total Cost : </span>Rs."+ totcost + "</div><div style='float:right;margin-right:5px'><span style='font-weight:700'>Total Items : </span>" + sum + "</div><div style='clear:both'></div>");
}
//slider2
var myPicIndex = 0;
picCarousel();
function picCarousel() {
var i;
var x = getElementsByClassName("myPicSlides");
for (i = 0; i < x.length; i++) {
x[i].style.display = "none";
}
myPicIndex++;
if (myPicIndex > x.length) {myPicIndex = 1}
x[myPicIndex-1].style.display = "block";
setTimeout(picCarousel, 3000); // Change image every 2 seconds
}
function getElementsByClassName(className) {
var found = [];
var elements = document.getElementsByTagName("*");
for (var i = 0; i < elements.length; i++) {
var names = elements[i].className.split(' ');
for (var j = 0; j < names.length; j++) {
if (names[j] == className) found.push(elements[i]);
}
}
return found;
}
//slider1
var myIndex = 0;
carousel();
function carousel() {
var i;
var x = getElementsByClassName("mySlides");
for (i = 0; i < x.length; i++) {
x[i].style.display = "none";
}
myIndex++;
if (myIndex > x.length) {myIndex = 1}
x[myIndex-1].style.display = "block";
setTimeout(carousel, 3000); // Change image every 2 seconds
}
function getElementsByClassName(className) {
var found = [];
var elements = document.getElementsByTagName("*");
for (var i = 0; i < elements.length; i++) {
var names = elements[i].className.split(' ');
for (var j = 0; j < names.length; j++) {
if (names[j] == className) found.push(elements[i]);
}
}
return found;
}
EDIT 2
I have further narrowed down the problem to the slider2 JS functions which seem to be a problem. Because if I remove the slider html which i have put in a slider2.php file and am including into the tariff.php file, then the scroll behaves properly.
slider2.php
<div style="width:100%;margin:0 auto">
<img class="myPicSlides" src="images/header/clothes-drying-on-line-iv.jpg" alt="Laundry Clothes Drying">
<img class="myPicSlides" src="images/header/new/shirts-on-line-iv.jpg" alt="Laundry Foam">
<img class="myPicSlides" src="images/header/iron-and-clothes-iv.jpg" alt="Iron Clothes">
<img class="myPicSlides" src="images/header/woollens-iv.jpg" alt="Woollens Laundry">
<img class="myPicSlides" src="images/header/shirts-on-hanger-iv.jpg" alt="Laundry Shirts mylaundrywala">
</div>
EDIT 3
I believe the animate function is taking into consideration the heights of the images in the slider and adding them up ! How to resolve that ?

If you want to reach to the top of window, please use this:
$("html, body").animate({
scrollTop: 0
}, 500);
$('.tariff').offset().top gives position distance between top of body and top of div with class "tariff".
As a result, it covers that much distance when scrolled.
Please try like this.

Use this code.
$(document).ready(function () {
$('html, body').animate({
scrollTop: $('.tariff').offset().top + $('.tariff').height()
}, 'slow');
});

Check the fiddle its is working for me there. Let me know if this helps.
$("#scroll").click(function(e) {
$('html, body').animate({
scrollTop: $('.tariff').offset().top
}, 'slow');
});
Fiddle

Since I realized that it was the heights of the images in the slider which was being laid out one below the other by html rather than fading in and out one by one when javascript is called (which has a fractional delay), the animate function registers the page height including all the heights of the images ! And scrolls keeping those heights in consideration. That is why it was scrolling right down to the bottom. Instead of top of the div.
Though I was not able to find a js solution to the real problem, I managed to find a work around.
Finally, what I did was to delay the slider images loading by using 'load' function. And placed one static image there till slider loaded and then faded the static image out after slider images loaded.
During this period, the animate function picks up only the height of that one static image which is actually the height that div should have after all images have loaded.
Now the animate scroll function is scrolling to the top of the relevant div.
Thanks all for your efforts to help

Vanilla way
var el = document.getElementById('myelement');
el.scrollTop = el.scrollHeight;

Change scrollTop offset when scrolling up, and different offset on scrollDown

I got an issue, where I have an dynamic header that gets bigger when scrolling up and smaller when scrolling down and therefore needs to change scrollTop offsets.
So i've been looking around and tried with my no existent java skills with no success.
This jquery code:
$(document).on('click', 'a[href^="#"]', function(e) {
var id = $(this).attr('href');
var $id = $(id);
if ($id.length === 0) {
return;
}
e.preventDefault();
// top position relative to the document
var pos = $(id).offset().top-500; // move this one
$('body, html').animate({scrollTop: pos});
});
var iScrollPos = 0;
$(window).scroll(function () {
var iCurScrollPos = $(this).scrollTop();
if (iCurScrollPos > iScrollPos) {
var pos = $(id).offset().top-500; //here when scrolling down
} else {
var pos = $(id).offset().top-100; // Here when scrolling up
}
iScrollPos = iCurScrollPos;
});
I made a JS fiddle to show what I'm trying to achieve: https://jsfiddle.net/zq9y7nge/1/
So, Is it possible to change offset depending on scrolling up and down?

Setting data type value to an element when it reaches the top of the viewport

I have a hex colour value stored on each section and when a section reaches the top of the screen (-180px for the header) I want to assign a css property to the header element in order to change the text colour as you scroll through the sections. I am not getting any errors and I am having trouble debugging this issue.
http://www.amypreston.co.uk/
$(window).load(function() {
var $header = $("header");
var numberOfSections = $("section").length;
var sectionOffsets = [];
var sectionColour = $("section").eq(i).data("colour");
for(var i = 0; i < numberOfSections; i++) {
sectionOffsets.push($("section").eq(i).offset().top);
}
$(window).scroll(function() {
var scrollTop = $(this).scrollTop();
for(var i = 0; i < numberOfSections; i++) {
if(scrollTop > sectionOffsets[i] - 180) {
$header.css('color', 'sectionColour');
}
}
});
});

I dont know if it happened by accident, but the line
var sectionColour = $("section").eq(i).data("colour");
is out of place. it uses a variable i which is only defined in the window scroll handler.
notice that you need to retrieve the section color each time the scroll handler runs, and not only on window load. you need to place this line from above in the loop inside the scroll handler.
Plus, as stated on the comments, you need to use the sectionColour as a variable, and not as a string like you do now. the single quote marks must be removed, so 'sectionColour' turns into sectionColour.
here is your fixed code:
$(window).load(function() {
var $header = $("header");
var numberOfSections = $("section").length;
var sectionOffsets = [];
for(var i = 0; i < numberOfSections; i++) {
sectionOffsets.push($("section").eq(i).offset().top);
}
$(window).scroll(function() {
var scrollTop = $(this).scrollTop();
for(var i = 0; i < numberOfSections; i++) {
if(scrollTop > sectionOffsets[i] - 180) {
var sectionColour = $("section").eq(i).data("colour");
$header.css('color', sectionColour);
}
}
});
});
On a side note, you could shorten your code into this:
$(window).scroll(function () {
$("section").each(function () {
if ($(window).scrollTop() > $(this).offset().top - 180) {
$("header").css('color', $(this).data("colour"));
}
});
}).scroll();

Javascript-only smooth scroll on button press

This site has a full-height image to start. Further content is located below the fold, with a 'scroll' element at the bottom of the image to prompt users to discover the rest of the content. On click, I've succeeded in making the site scroll down by 300 pixels. I want to do this smoothly, however. Here is my current code:
window.onload = function () {
var scroll = document.getElementById("scroll");
scroll.onclick = function () {
var top = self.pageYOffset;
var goal = 300;
for(var i=0, l=goal; i<l; ++i) {
window.scrollBy(0,1);
}
};
};
This works for scrolling, but not smoothly. I thought that if I had the for loop, changing the window.scrollBy value to something like .001 would make it scroll more slowly (thus, smoothly), but that function doesn't seem to take decimal points.
Any tips? Technically it's fine now, but I'd rather add that last bit of polish. Thanks!

Your code runs very fast and you don't see a smooth effect. You must use the setInterval() function, and scroll to the 300/n px in each iteration (n - number of iterations). Like this:
window.onload = function () {
var scroll = document.getElementById("scroll");
scroll.onclick = function () {
var currentScroll = 0;
var goal = 300;
var step = goal/10
var timer = setInterval( function () {
if (currentScroll < goal) {
window.scrollBy(0, step);
currentScroll += step;
} else {
clearInterval(timer);
}
}, 50);
};
};

Try something like this...example
$(function() {
$('a[href*=#]:not([href=#])').click(function() {
if (location.pathname.replace(/^\//,'') == this.pathname.replace(/^\//,'') && location.hostname == this.hostname) {
var target = $(this.hash);
target = target.length ? target : $('[name=' + this.hash.slice(1) +']');
if (target.length) {
$('html,body').animate({
scrollTop: target.offset().top
}, 1000);
return false;
}
}
});
});