Slide header up if you scroll down and vice versa

Question

Update

I made a repo on GitHub:

https://github.com/yckart/Veil.js

Big thanks to Sargo Darya and Edward J Payton.

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I've to create a header which slides up if you scroll down and vice versa. The problem is, that it jumps (if you are in the diff-range between 0-128).

I can not figure out where the problem sits. Any idea how to get this to work correctly?

Here's what I've done so far: http://jsfiddle.net/yckart/rKW3f/

// something simple to get the current scroll direction
// false === down | true === up
var scrollDir = (function (oldOffset, lastOffset, oldDir) {
    return function (offset) {
        var dir = offset < oldOffset;
        if (dir !== oldDir) lastOffset = offset;
        oldOffset = offset;
        oldDir = dir;
        return {dir: dir, last: lastOffset};
    };
}());

var header = document.querySelector('header');
var height = header.clientHeight;
addEventListener('scroll', function () {
    var scrollY = document.documentElement.scrollTop || document.body.scrollTop;
    var dir = scrollDir(scrollY);
    var diff = dir.last-scrollY;

    var max = Math.max(-height, Math.min(height, diff));
    header.style.top = (dir.dir ? max-height : max) + 'px';
});

Another problem is, that if the scroll-direction was changed the first time, nothing happens. However, this could be fixed with an interval, or else.

Answer 1

Try this out:- http://jsfiddle.net/adiioo7/rKW3f/7/

JS:-

var scrollDir = (function (oldOffset, lastOffset, oldDir) {
    return function (offset) {

        var dir = offset < oldOffset;
        if (dir !== oldDir) {
            lastOffset = offset;
        } else {
            offset = offset - height;
        }
        oldOffset = offset;
        oldDir = dir;
        return {
            dir: dir,
            last: lastOffset
        };
    };
}());

var header = document.querySelector('header');
var height = header.clientHeight;

$(window).scroll(function () {
    var scrollY = $(window).scrollTop();
    var dir = scrollDir(scrollY);
    var diff = dir.last - scrollY;

    var max = Math.max(-height, Math.min(height, diff));

    max = (dir.dir ? max - height : max); 
    max = scrollY<height?0:max;


    $('header').data('size', 'small');
    $('header').stop().animate({
        top: max
    }, 600);


});

Answer 2

I believe this is exactly what you want:

var header = $('header'),
headerHeight = header.height(),
treshold = 0,
lastScroll = 0;

$(document).on('scroll', function (evt) {
    var newScroll = $(document).scrollTop(),
        diff = newScroll-lastScroll;

    // normalize treshold range
    treshold = (treshold+diff>headerHeight) ? headerHeight : treshold+diff;
    treshold = (treshold < 0) ? 0 : treshold;

    header.css('top', (-treshold)+'px');

    lastScroll = newScroll;
});

Demo on: http://jsfiddle.net/yDpeb/

Answer 3

Sargo Darya's answer above is exacty what i was looking for but I found a bug with Webkits inertia scrolling so I made a fix:

// Scrolling Header
var header = $('header'),
headerHeight = header.height(),
offset = 0,
lastPos = 0;

$(document).on('scroll', function(e) {
var newPos = $(document).scrollTop(),
    pos = newPos-lastPos;

if (offset+pos>headerHeight) { 
    offset = headerHeight;
} else if (newPos < 0){ // webkit inertia scroll fix
    offset = 0;
} else {
    offset = offset+pos;
};
if (offset < 0) {
    offset = 0;
} else {
    offset = offset;
};

header.css('top', (-offset)+'px');

lastPos = newPos;
});

Adding one line fixed it. If - if scroll position is lower than 0, set header offset at 0.

Demo based on Sargo Darya's - http://jsfiddle.net/edwardomni/D58vx/4/