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Detecting scroll direction

So I am trying to use the JavaScript on scroll to call a function. But I wanted to know if I could detect the direction of the the scroll without using jQuery. If not then are there any workarounds?
I was thinking of just putting a 'to top' button but would like to avoid that if I could.
I have now just tried using this code but it didn't work:
if document.body.scrollTop <= 0 {
alert ("scrolling down")
} else {
alert ("scrolling up")
}

It can be detected by storing the previous scrollTop value and comparing the current scrollTop value with it.
JavaScript :
var lastScrollTop = 0;
// element should be replaced with the actual target element on which you have applied scroll, use window in case of no target element.
element.addEventListener("scroll", function(){ // or window.addEventListener("scroll"....
var st = window.pageYOffset || document.documentElement.scrollTop; // Credits: "https://github.com/qeremy/so/blob/master/so.dom.js#L426"
if (st > lastScrollTop) {
// downscroll code
} else if (st < lastScrollTop) {
// upscroll code
} // else was horizontal scroll
lastScrollTop = st <= 0 ? 0 : st; // For Mobile or negative scrolling
}, false);

Simple way to catch all scroll events (touch and wheel)
window.onscroll = function(e) {
// print "false" if direction is down and "true" if up
console.log(this.oldScroll > this.scrollY);
this.oldScroll = this.scrollY;
}

Use this to find the scroll direction. This is only to find the direction of the Vertical Scroll. Supports all cross browsers.
var scrollableElement = document.body; //document.getElementById('scrollableElement');
scrollableElement.addEventListener('wheel', checkScrollDirection);
function checkScrollDirection(event) {
if (checkScrollDirectionIsUp(event)) {
console.log('UP');
} else {
console.log('Down');
}
}
function checkScrollDirectionIsUp(event) {
if (event.wheelDelta) {
return event.wheelDelta > 0;
}
return event.deltaY < 0;
}
Example

You can try doing this.
function scrollDetect(){
var lastScroll = 0;
window.onscroll = function() {
let currentScroll = document.documentElement.scrollTop || document.body.scrollTop; // Get Current Scroll Value
if (currentScroll > 0 && lastScroll <= currentScroll){
lastScroll = currentScroll;
document.getElementById("scrollLoc").innerHTML = "Scrolling DOWN";
}else{
lastScroll = currentScroll;
document.getElementById("scrollLoc").innerHTML = "Scrolling UP";
}
};
}
scrollDetect();
html,body{
height:100%;
width:100%;
margin:0;
padding:0;
}
.cont{
height:100%;
width:100%;
}
.item{
margin:0;
padding:0;
height:100%;
width:100%;
background: #ffad33;
}
.red{
background: red;
}
p{
position:fixed;
font-size:25px;
top:5%;
left:5%;
}
<div class="cont">
<div class="item"></div>
<div class="item red"></div>
<p id="scrollLoc">0</p>
</div>

Initialize an oldValue
Get the newValue by listening to the event
Subtract the two
Conclude from the result
Update oldValue with the newValue
// Initialization
let oldValue = 0;
//Listening on the event
window.addEventListener('scroll', function(e){
// Get the new Value
newValue = window.pageYOffset;
//Subtract the two and conclude
if(oldValue - newValue < 0){
console.log("Up");
} else if(oldValue - newValue > 0){
console.log("Down");
}
// Update the old value
oldValue = newValue;
});

This is an addition to what prateek has answered.There seems to be a glitch in the code in IE so i decided to modify it a bit nothing fancy(just another condition)
$('document').ready(function() {
var lastScrollTop = 0;
$(window).scroll(function(event){
var st = $(this).scrollTop();
if (st > lastScrollTop){
console.log("down")
}
else if(st == lastScrollTop)
{
//do nothing
//In IE this is an important condition because there seems to be some instances where the last scrollTop is equal to the new one
}
else {
console.log("up")
}
lastScrollTop = st;
});});

While the accepted answer works, it is worth noting that this will fire at a high rate. This can cause performance issues for computationally expensive operations.
The recommendation from MDN is to throttle the events. Below is a modification of their sample, enhanced to detect scroll direction.
Modified from: https://developer.mozilla.org/en-US/docs/Web/API/Document/scroll_event
// ## function declaration
function scrollEventThrottle(fn) {
let last_known_scroll_position = 0;
let ticking = false;
window.addEventListener("scroll", function () {
let previous_known_scroll_position = last_known_scroll_position;
last_known_scroll_position = window.scrollY;
if (!ticking) {
window.requestAnimationFrame(function () {
fn(last_known_scroll_position, previous_known_scroll_position);
ticking = false;
});
ticking = true;
}
});
}
// ## function invocation
scrollEventThrottle((scrollPos, previousScrollPos) => {
if (previousScrollPos > scrollPos) {
console.log("going up");
} else {
console.log("going down");
}
});

This simple code would work: Check the console for results.
let scroll_position = 0;
let scroll_direction;
window.addEventListener('scroll', function(e){
scroll_direction = (document.body.getBoundingClientRect()).top > scroll_position ? 'up' : 'down';
scroll_position = (document.body.getBoundingClientRect()).top;
console.log(scroll_direction);
});

You can get the scrollbar position using document.documentElement.scrollTop. And then it is simply matter of comparing it to the previous position.

If anyone looking to achieve it with React hooks
const [scrollStatus, setScrollStatus] = useState({
scrollDirection: null,
scrollPos: 0,
});
useEffect(() => {
window.addEventListener("scroll", handleScrollDocument);
return () => window.removeEventListener("scroll", handleScrollDocument);
}, []);
function handleScrollDocument() {
setScrollStatus((prev) => { // to get 'previous' value of state
return {
scrollDirection:
document.body.getBoundingClientRect().top > prev.scrollPos
? "up"
: "down",
scrollPos: document.body.getBoundingClientRect().top,
};
});
}
console.log(scrollStatus.scrollDirection)

I personally use this code to detect scroll direction in javascript...
Just you have to define a variable to store lastscrollvalue and then use this if&else
let lastscrollvalue;
function headeronscroll() {
// document on which scroll event will occur
var a = document.querySelector('.refcontainer');
if (lastscrollvalue == undefined) {
lastscrollvalue = a.scrollTop;
// sets lastscrollvalue
} else if (a.scrollTop > lastscrollvalue) {
// downscroll rules will be here
lastscrollvalue = a.scrollTop;
} else if (a.scrollTop < lastscrollvalue) {
// upscroll rules will be here
lastscrollvalue = a.scrollTop;
}
}

Modifying Prateek's answer, if there is no change in lastScrollTop, then it would be a horizontal scroll (with overflow in the x direction, can be used by using horizontal scrollbars with a mouse or using scrollwheel + shift.
const containerElm = document.getElementById("container");
let lastScrollTop = containerElm.scrollTop;
containerElm.addEventListener("scroll", (evt) => {
const st = containerElm.scrollTop;
if (st > lastScrollTop) {
console.log("down scroll");
} else if (st < lastScrollTop) {
console.log("up scroll");
} else {
console.log("horizontal scroll");
}
lastScrollTop = Math.max(st, 0); // For mobile or negative scrolling
});

This seems to be working fine.
document.addEventListener('DOMContentLoaded', () => {
var scrollDirectionDown;
scrollDirectionDown = true;
window.addEventListener('scroll', () => {
if (this.oldScroll > this.scrollY) {
scrollDirectionDown = false;
} else {
scrollDirectionDown = true;
}
this.oldScroll = this.scrollY;
// test
if (scrollDirectionDown) {
console.log('scrolling down');
} else {
console.log('scrolling up');
}
});
});

Sometimes there are inconsistencies in scrolling behavior which does not properly update the scrollTop attribute of an element. It would be safer to put some threshold value before deciding the scroll direction.
let lastScroll = 0
let threshold = 10 // must scroll by 10 units to know the direction of scrolling
element.addEventListener("scroll", () => {
let newScroll = element.scrollTop
if (newScroll - lastScroll > threshold) {
// "up" code here
} else if (newScroll - lastScroll < -threshold) {
// "down" code here
}
lastScroll = newScroll
})

let arrayScroll = [];
window.addEventListener('scroll', ()=>{
arrayScroll.splice(1); //deleting unnecessary data so that array does not get too big
arrayScroll.unshift(Math.round(window.scrollY));
if(arrayScroll[0] > arrayScroll[1]){
console.log('scrolling down');
} else{
console.log('scrolling up');
}
})
I have self-made the above solution. I am not sure if this solution may cause any considerable performance issue comparing other solutions as I have just started learning JS and not yet have completed my begginer course. Any suggestion or advice from experienced coder is highly appriciated. ThankYou!

Enable scroll within a function

When I use scrollWheel I'm incremeting the currentSlide by one, when currentSlide === 2 the red div is going up and I want to enable the scrolling to the body. As you see my bind function is returning false. I tried to put conditions on that and return true when currentSlide === 2 but apparently it won't work.
Can anybody explain to me how to fix that?
var currentSlide = 0;
function scrollDown() {
console.log('Scroll Down', currentSlide);
if(currentSlide < 3) {
currentSlide += 1;
}
if(currentSlide === 3) {
$('#el').addClass('hide');
}
}
http://jsbin.com/rovicawija/1/edit?js,console,output

Technically you are hiding the element when currentSlide is equal to 3 not 2.
Anyways instead of return false; in the bindings you will want to do return currentSlide >= 3; so that when the red div is hidden you can now scroll.
Also as someone else noted use on instead of bind because bind has been deprecated.

I'm totally not sure what you are trying to do as your question and expected result is quite unclear
I made the code as following
var currentSlide = 0;
function scrollDown() {
console.log('Scroll Down', currentSlide);
if(currentSlide < 10) {
currentSlide += 1;
return false;
}
if(currentSlide === 10) {
$('#el').addClass('hide');
}
}
$(window).on('DOMMouseScroll', function(e) {
if (e.originalEvent.detail > 0) {
return scrollDown();
}
})
.on('mousewheel', function(e) {
if (e.originalEvent.wheelDelta < 0) {
return scrollDown();
}
});
By using on(which you should) and having the scrollDown returning a boolean false if not good to go, and return nothing if there's nothing to do.

I just put return true on the last function and everything seemed to work fine, see here:
$(window).bind('DOMMouseScroll', function(e) {
if (e.originalEvent.detail > 0) {
scrollDown();
}
return false;
})
.bind('mousewheel', function(e) {
if (e.originalEvent.wheelDelta < 0) {
scrollDown();
}
return true;
});

Trying to debug a custom .sort in a JS array

A link to the Plunker.
I've been working on a button and list system in jQuery for awhile now. Recently I decided to make my code more reproducible. I want to make it so I just have to add classes or IDs, and I don't have to add any additional code. I'm very close to doing that for my entire site. So if you go to this site specifically you will see it in action.
If you click on any buttons, in any order, it will arrange chronologically.
The bugs come from closing them.
If you click at least three, close the middle one, then click a new button, the sort function falls apart and that closed middle one is now floating with the wrong class.
Below is my current jQuery. On my site, ignore the "All Years" button. I'll work on that after I figure out this bug.
//the variables needed for the floating buttons
var groupArray = $(".yearGroup");
var buttonArray = $(".buttonGroup");
var hideGroupArray = $(".hideGroup");
var closeBarArray = $(".closeBar");
var closeBar = $("#allCloseBar");
var allButtonArray = [];
sortElements = function(a,b)
{
if (a.text() < b.text())
{
return -1;
}
else if (a.text() > b.text())
{
return 1;
}
else
{
return 0;
}
}
$.each(buttonArray, function(i, item) {
$(this).click(function(){
console.log($(buttonArray[i]).text())
console.log($(closeBarArray[i]).text())
//for removing the tooltip when the button is clicked. Mostly for Firefox bug
$(".ui-tooltip-content").parents('div').remove();
$(hideGroupArray[i-1]).slideToggle(slideToggleDuration, function(){
htmlBody.animate({scrollTop: $(groupArray[i-1]).offset().top - 25}, {duration: timeDuration, easing: 'easeOutBack'});
$(buttonArray[i]).toggleClass("float", 1200);
if ($(groupArray[i-1]).height() > 0)
{
//This will stop any animations if the user scrolls.
htmlBody.bind("scroll mousedown DOMMouseScroll mousewheel keyup", function(e)
{
if ( e.which > 0 || e.type === "mousedown" || e.type === "mousewheel"){
htmlBody.stop().unbind('scroll mousedown DOMMouseScroll mousewheel keyup');
}
});
closeBar.addClass("floatCloseBar");
$(closeBarArray[i]).hide();
allButtonArray.splice(0, 0, $(buttonArray[i]));
var timer;
var delay = 1500;
$(buttonArray[i]).hover(function() {
//This will stop any animations if the user scrolls.
htmlBody.bind("scroll mousedown DOMMouseScroll mousewheel keyup", function(e)
{
if ( e.which > 0 || e.type === "mousedown" || e.type === "mousewheel"){
htmlBody.stop().unbind('scroll mousedown DOMMouseScroll mousewheel keyup');
}
});
var link = $(groupArray[i-1]);
var offset = link.offset();
var top2 = offset.top;
var left = offset.left;
var bottom = top2 + $(groupArray[i-1]).outerHeight();
//bottom = Math.abs(bottom - offset.top);
var right = $(window).width() - link.width();
right = Math.abs(offset.left - right);
var scrollDuration = 0;
if (inRange($(buttonArray[i]).offset().top, $(groupArray[i-1]).position().top, bottom))
{
//console.log("fast");
scrollDuration = 500;
//$(group).addClass("hoverYear");
}
else if ($(buttonArray[i]).offset().top <= $(groupArray[i-1]).offset().top && allButtonArray.length == 1)
{
//console.log("fast");
scrollDuration = 500;
//$(group).removeClass("hoverYear");
}
else if ($(buttonArray[i]).offset().top > 495 && $(buttonArray[i]).offset().top < 1700 && !inRange($(buttonArray[i]).offset().top, $(groupArray[i-1]).position().top, bottom))
{
scrollDuration = 1000;
//console.log("slow");
//$(group).removeClass("hoverYear");
}
else if ($(buttonArray[i]).offset().top > 1701 && $(buttonArray[i]).offset().top < 3000 && !inRange($(buttonArray[i]).offset().top, $(groupArray[i-1]).position().top, bottom))
{
scrollDuration = 1500;
//console.log("slower");
//$(group).removeClass("hoverYear");
}
else if ($(buttonArray[i]).offset().top > 3001 && $(buttonArray[i]).offset().top < 6000 && !inRange($(buttonArray[i]).offset().top, $(groupArray[i-1]).position().top, bottom))
{
scrollDuration = 2000;
//console.log("much slower");
//$(group).removeClass("hoverYear");
}
else if ($(buttonArray[i]).offset().top > 6001 && !inRange($(buttonArray[i]).offset().top, $(groupArray[i-1]).position().top, bottom))
{
scrollDuration = 2500;
console.log("the slowest");
//$(group).removeClass("hoverYear");
}
else
{
scrollDuration = 500;
}
//to prevent the various hover states to take control when the button isn't floating
if (!($(buttonArray[i])).hasClass("float"))
{
scrollDuration = 0;
console.log("doesnt have class")
}
// on mouse in, start a timeout
timer = setTimeout(function() {
//the delay for the hover scroll feature
htmlBody.animate({scrollTop: $(groupArray[i-1]).offset().top}, scrollDuration, 'easeInOutCubic');
}, delay);
}, function() {
// on mouse out, cancel the timer
clearTimeout(timer);
});
$.each(allButtonArray, function(j, val){
$(allButtonArray[j]).appendTo(closeBar);
console.log(allButtonArray.length);
arrowDown.show();
arrowUp.show();
arrowDown.prependTo(closeBar);
arrowUp.appendTo(closeBar);
//Changes the width of the buttons based upon how many are on the screen
if (allButtonArray.length > 7)
{
$("float").css('width', '7%');
$(val).css('width', '7%');
$(allButtonArray[0]).css('width','7%');
allButtonArray.sort(sortElements);
//console.log(val);
}
else if (allButtonArray.length <= 7)
{
$(val).css("width", '10%');
$("float").css("width", '10%');
allButtonArray.sort(sortElements);
//console.log(val);
}
});
}
if ($(groupArray[i-1]).height() == 0)
{
$(buttonArray[i]).css("width", '50%');
allButtonArray.splice(allButtonArray.indexOf($(buttonArray[i])), 1);
console.log(allButtonArray.length);
$(closeBarArray[i]).show();
$(buttonArray[i]).appendTo($(closeBarArray[i]));
arrowDown.show();
arrowUp.show();
arrowDown.prependTo(closeBar);
arrowUp.appendTo(closeBar);
}
if (group2001.height() == 0 && group2002.height() == 0 && group2003.height() == 0 && group2004.height() == 0 && group2005.height() == 0 && group2006.height() == 0 && group2007.height() == 0
&& group2008.height() == 0 && group2009.height() == 0 && group2010.height() == 0 && group2011.height() == 0 && group2012.height() == 0)
{
$(closeBarArray[i]).removeClass("floatCloseBar");
htmlBody.animate({scrollTop: revealAllButton.offset().top - 75}, 500);
arrowDown.hide();
arrowUp.hide();
//console.log($(document).height() + " the current height");
}
});
$(buttonArray[i]).toggleClass("openClose");
$(buttonArray[i]).toggleClass("openClose2");
});
});
function inRange(x, min, max){
return (x >= min && x <= max);
}
If you would like a reference to what worked previously, I could post that code. It is much more bulky and much less organized. I've tried many different things to eliminate the bug but I'm at a loss. My knowledge of JS scope is limited.
And thanks for any help, it is very much appreciated.

Autoscroll was but now isn't working

I was working on a project that, when you click the page, it scrolls the entire length of the page. But it does this at 20px intervals; this is to allow javascript to be executed while scrolling in iOS.
However, when uploading the final version, my ftp client has deleted some of the code and it's now not working. I can't see why.
Any suggestions?
var t;
var scrolling = false;
// doScroll sets the position in which to auto pause.
function doScroll() {
$('body').scrollTop($('body').scrollTop() + 20);
if($("#pause").offset().top >=300 && $("#pause").offset().top < 304){
ScrollIt();
} else
if($("#pause").offset().top >=4000 && $("#pause").offset().top < 4004){
ScrollIt() ;
} else
if($("#pause").offset().top >=7500 && $("#pause").offset().top < 7504){
ScrollIt() ;
}
}
// ScrollIt removes the interval for scrolling, pausing the scroll.
function ScrollIt() {
clearInterval(t);
scrolling = false;
return;
// playPause()
}
//Stop/start on click
$('#pause').on('click',function(){
ScrollIt();
scrolling = !scrolling;
if(!scrolling){
clearInterval(t);
return;
}
t = setInterval(doScroll, 5);
});

I create jsfiddle page for you.
http://jsfiddle.net/u32Nw/2/
I can see that it is working, but scrolling is not stopping.
var t;
var scrolling = false;
// doScroll sets the position in which to auto pause.
function doScroll() {
var $body = $("body"),
$pause = $("#pause");
$body.scrollTop($body.scrollTop() + 20);
var pauseTop = $pause.offset().top;
if (pauseTop >= 300 && pauseTop < 304 || pauseTop >= 4000 && pauseTop < 4004 || pauseTop >= 7500 && pauseTop < 7504) {
clearScrollInterval();
}
}
// scrollIt removes the interval for scrolling, pausing the scroll.
function clearScrollInterval() {
clearInterval(t);
scrolling = false;
return;
// playPause()
}
//Stop/start on click
$("#pause").on("click", function () {
clearScrollInterval();
scrolling = !scrolling;
t = setInterval(doScroll, 5);
});
This is exact same code, just refactored.
Try working from here. You need to refactor your code for debugging.

Subtract from an integer using jquery

I want to scroll to a div each time user presses j key. Here is the code for it.
$(function() {
function scroll(direction) {
var scroll, i,
positions = [],
here = $(window).scrollTop(),
collection = $('.message_box');
collection.each(function() {
positions.push(parseInt($(this).offset()['top'],0));
});
for(i = 0; i < positions.length; i++) {
if (direction == 'next' && positions[i] > here) { scroll = collection.get(i); break; }
if (direction == 'prev' && i > 0 && positions[i] >= here) { scroll = collection.get(i); break; }
}
if (scroll) {
$('html, body').animate({"scrollTop": $(scroll).offset().top-50});
$(scroll).css('color', 'blue');
$(scroll).mouseleave(function() {
$(this).css('color', 'black');
});
}
return false;
}
$("#next,#prev").click(function() {
return scroll($(this).attr('id'));
});
$('body').keyup(function(event) {
if (event.which == 74) {
return scroll('next');
}
});
$('body').keyup(function(event) {
if (event.which == 75) {
return scroll('prev');
}
});
});
I need to subtract 50 from the offest of the div to scroll to which is this.
$('html, body').animate({"scrollTop": $(scroll).offset().top-50});
It will scroll the first time but not the rest of the times. I always get the integer 218 which is the offset of the first div to scroll to.
DEMO - http://jsfiddle.net/XP5sP/6/
Can someone help me ?

The problem is that you're always moving the scrollTop value to 50 pixels before the first matched element, so it's always identifying that element as the one you need to scroll to in your if statement because its position is greater than the current scrollTop value.
Modify the relevant section of your code to this:
if (direction == 'next' && positions[i] > here + 50) {
scroll = collection.get(i);
break;
}
That way it accounts for the window being scrolled to 50 pixels above the current element.

$(scroll).offset().top-50 is prefectly valid, as .top will return an integer value. Therefore the issue is not with this portion of your code.
I suspect the issue is to do with the scroll variable you have within the scroll function. I always keep away from naming my variables the same as my function names when within the same scope.

Try putting some space between your minus symbol so it does not get mistaken for a dash.
$('html, body').animate({"scrollTop": $(scroll).offset().top - 50});
or save your mathematics in a variable first
var scrollMinusFifty = $(scroll).offset().top - 50;
$('html, body').animate({"scrollTop":scrollMinusFifty});