Develop Reference

On scroll up/down trigger a function once

I need to load 2 different animated graphic on window scroll up/down on a website by triggering some functions, it's working but its buggy as the functions are triggered too many times when scrolling:
$(window).scroll(function() {
var scroll = $(window).scrollTop(),
headerHeight = $('.navbar').outerHeight();
if(scroll > headerHeight) {
loadLogoAnimeDown();
}else{
loadLogoAnimeUp();
}
});

You need a way to check if the functions have been called (and logo has been loaded), so you can use a variable for that. After the logo has been loaded, you set the variable as false, which prevents them from loading more than once.
var downNotLoaded = true;
var upNotLoaded = true;
$(window).scroll(function() {
var scroll = $(window).scrollTop(),
headerHeight = $('.navbar').outerHeight();
if(scroll > headerHeight) {
if(downNotLoaded){
loadLogoAnimeDown();
downNotLoaded = false;
}
}else{
if(upNotLoaded){
loadLogoAnimeUp();
upNotLoaded = false;
}
}
});

I think you might find this is a very hacky way to do it, but this should work.
var animated;
$(window).scroll(function() {
var scroll = $(window).scrollTop(),
headerHeight = $('.navbar').outerHeight();
if(scroll > headerHeight) {
if (animated == true) {
loadLogoAnimeDown();
animated = false;
}
} else{
if (animated == false) {
loadLogoAnimeUp();
animated = true;
}
}
});

Why is jQuery removeClass reappearing on scroll?

I have a div with a 2 logos in it and on scroll the first logo hides and the second appears using classes. On reverse scroll the second logo should hide and the first reappear. The first is reappearing but the second is hiding then reappearing when I reach the top of the page.
I've been going around in circles and I can't understand why on reverse scroll the 'show-logo' class is reappearing. Can anyone explain why?
JS:
if ($(window).width() > 640){
var scrollTop = $(window).scrollTop();
var header = $(".site-header");
if (scrollTop > 50) {
header.addClass("scrolling");
setTimeout(function() {
header.addClass("show-logo");
}, 500);
}
else {
header.removeClass("show-logo scrolling");
};
} else {
header.removeClass("show-logo scrolling");
}
Thanks in advance.

The setTimeout has no clue that it should not run so it runs. So if you do not want it to execute it, you need to cancel it. Two different ways depending on what you want to happen.
var myTimer = null;
var header = $(".site-header");
var win = $(window);
win.on("scroll", function() {
if (myTimer) {
window.clearTimeout(myTimer)
}
if ($(win.width() > 640) {
var scrollTop = win.scrollTop();
if (scrollTop > 50) {
header.addClass("scrolling");
myTimer = setTimeout(function() {
header.addClass("show-logo");
}, 500);
} else {
header.removeClass("show-logo scrolling");
}
} else {
header.removeClass("show-logo scrolling");
}
});
or
var myTimer = null;
var header = $(".site-header");
var win = $(window);
win.on("scroll", function() {
if ($(win.width() > 640) {
var scrollTop = win.scrollTop();
if (scrollTop > 50) {
header.addClass("scrolling");
if (!myTimer) {
myTimer = setTimeout(function() {
header.addClass("show-logo");
}, 500);
}
} else {
header.removeClass("show-logo scrolling");
if (myTimer) {
window.clearTimeout(myTimer)
myTimer = null
}
}
} else {
header.removeClass("show-logo scrolling");
}
});

Toggle mobile navigation depending on scroll direction

I have this navigation for mobile that i want to hide/show depending on which direction the viewport gets scrolled in. So if scrolling down i want it to hide, and scrolling up i want it to show.
My current code looks like this. It just toggles on scroll top. Anyone?
$(function() {
$(window).on("scroll touchmove", function () {
$('.mobile-nav').toggleClass('tiny', $(document).scrollTop() > 0);
});
});

Maybe something like this:
var menu_height = 80;
var menu_visible = true;
var old_scroll = $(window).scrollTop();
function checkMenu() {
new_scroll = $(window).scrollTop();
if (old_scroll < new_scroll && new_scroll > 0) {
// Scroll down
if (menu_visible == true) {
toggleMenu();
}
} else if (old_scroll > new_scroll) {
// Scroll up
if (menu_visible != true) {
toggleMenu();
}
}
old_scroll = new_scroll;
}
function toggleMenu() {
if (menu_visible == true) {
// Hide
$('#menu').animate({top: '-='+menu_height+'px'}, 200, function(){ $(this).css('display', 'none') });
menu_visible = false;
} else {
// Show
menu_visible = true;
$('#menu').css('display', 'block').animate({top: '+='+menu_height+'px'}, 200);
}
}
$(document).ready(function() {
// Show / hide menu on scroll
setInterval(checkMenu, 100);
});
Codepen: http://codepen.io/anon/pen/dPGggg

Force "overscrolling" at Chrome/Mac with javascript

When you get to the limit of document, you can keep scrolling and can see an background behing the document before it bounces back (overscrolling).
How can I force the window to overscroll like this with javascript?

This is not the ultimate solution since I think the animation is imperfect and it's really only for desktops, but it can at least get you started. What I have done is increase the height of the body for animation on scroll.
$(document).on('scroll mousewheel', function (e) {
//Check for mousewheel scrolling down (or not used at all)
if (!e.originalEvent || !e.originalEvent.wheelDeltaY
|| e.originalEvent.wheelDeltaY < 0) {
if ($(window).height() + $(this).scrollTop() == $(this).height()) {
//Prevent simultaneous triggering of the animation
if (!$("body").data('bouncing')) {
$("body").height(function (_, h) { return h + 15; })
.data('bouncing', true);
$("body, html").animate({
'scrollTop': '+=15'
}, 125).animate({
'scrollTop': '-=15'
}, {duration: 125, complete: function () {
$(this).height(function (_, h) { return h - 15; })
.data('bouncing', false);
}});
}
}
}
}).on('keydown', function (e) {
//The "down" arrow; still bounces when pressed at the bottom of the page
if (e.which == '40') {
$(this).trigger('scroll');
}
});

I've been playing with this version that imitates the effect using a div, that slides in and out of view at the bottom of the page. If you have a high res monitor, you may need to increase the height of the main div to test it.
<div id="main" style="background:#f5f5f5;height:1000px"></div>
<div id="overscroll" style="background:#666666;height:120px"></div>
<script type="text/javascript">
var $doc = $(document);
$doc.ready(function () {
var $wnd = $(window),
$oscroll = $('#overscroll'),
block = false;
$wnd.bind('scroll', function () {
if (!block) {
block = true;
var scrollTop = $wnd.scrollTop(),
wndHeight = $wnd.height(),
docHeight = $doc.height();
try {
if (scrollTop + (wndHeight + 120) > docHeight) {
$oscroll.slideUp('slow');
}
else if ($oscroll.css('display') === 'none'
&& (scrollTop + (wndHeight + 120) < docHeight)) {
$oscroll.slideDown();
}
} finally {
block = false;
}
}
});
});
</script>

Add class to element upon scroll

I'd like to add a class to an element when a user first scrolls away from the top of the page. If the user then scrolls back up and hits the top of the page I'd like that class removed.
Use of jQuery in the solution is fine.

try
$(window).scroll(function() {
$("id or class").removeClass("active");
var scroll = $(window).scrollTop();
if (scroll <= 500) {
$("#one").addClass("active");
}
else if (scroll <= 1000) {
$("#tow").addClass("active");
}
else {
$("#three").addClass("active");
}
}

So here is the solution you're looking for. Just customize it with your div tags.
$(document).ready(function () {
$(window).scroll(function(){
// get the height of #wrap
var h = $('#top').height();
var y = $(window).scrollTop();
if( y > (h*.25) ){
$("#sidef").fadeIn(1100);
} else {
$('#sidef').fadeOut(75);
}
});
});

var notAdded = true;
$(window).scroll(function(){
if( $(this).scrollTop() == 0){
$(elem).removeClass('classname');
notAdded = true;
}
else if(notAdded){
$(elem).addClass('classname');
notAdded = false;
}
});