Change Element Style On Page Scroll

Question

I want to change the visibility of an element after the user scrolls down 100px.

I have some code already,

var fixed = false;
$(document).scroll(function() {
    if( $(this).scrollTop() >= 100 ) {
        if( !fixed ) {
            fixed = true;
            $('#logo-scroll').css({position:'fixed', display:'visible !important'});
        }
    } else {
        if( fixed ) {
            fixed = false;
            $('#logo-scroll').css({display:'none'});
        }
    }
});​

JSFiddle.

The code has two problems.

1. It doesn't default to be invisible, I want it so it starts invisible.

2. It doesn't repeat, when the user scrolls back up, it doesn't go back being invisible.

More details,

I want to make something like this header, but, as you can see, there's a certain point where you see half of the small logo, and a PART of the bigger one. It doesn't affect techcrunch much as the header is small, but on my site, it does. I have made everything, I just need to start it in display:none, and become visible after 100px.

Answer 1

Use: display:block; and display:none;

jsFiddle DEMO

Add this to your CSS:

#logo-scroll{ display:none; position:fixed; }

jQ:

var $logo = $('#logo-scroll');
$(document).scroll(function() {
    $logo.css({display: $(this).scrollTop()>100 ? "block":"none"});
});

BTW: on TC page it's just a CSS play with z-indexes. nothing more. all elements are visible at page load, it's just the scroll that makes appear a z-index lower element beneath the big logo.

In plain Javascript would be like this:

var win = window,
    docEl = document.documentElement,
    $logo = document.getElementById('logo-scroll');

win.onscroll = function(){
   var sTop = (this.pageYOffset || docEl.scrollTop)  - (docEl.clientTop || 0);
   $logo.style.display =  sTop > 100 ? "block":"none" ;
};

Answer 2

Well the question has already been answered. just adding a better example which might be useful for others and it's exactly what op wants.

code and demo

Edited: Added actual code from original source.

jQuery:

// This function will be executed when the user scrolls the page.
$(window).scroll(function(e) {
    // Get the position of the location where the scroller starts.
    var scroller_anchor = $(".scroller_anchor").offset().top;

    // Check if the user has scrolled and the current position is after the scroller start location and if its not already fixed at the top 
    if ($(this).scrollTop() >= scroller_anchor && $('.scroller').css('position') != 'fixed') 
    {    // Change the CSS of the scroller to hilight it and fix it at the top of the screen.
        $('.scroller').css({
            'background': '#CCC',
            'border': '1px solid #000',
            'position': 'fixed',
            'top': '0px'
        });
        // Changing the height of the scroller anchor to that of scroller so that there is no change in the overall height of the page.
        $('.scroller_anchor').css('height', '50px');
    } 
    else if ($(this).scrollTop() < scroller_anchor && $('.scroller').css('position') != 'relative') 
    {    // If the user has scrolled back to the location above the scroller anchor place it back into the content.

        // Change the height of the scroller anchor to 0 and now we will be adding the scroller back to the content.
        $('.scroller_anchor').css('height', '0px');

        // Change the CSS and put it back to its original position.
        $('.scroller').css({
            'background': '#FFF',
            'border': '1px solid #CCC',
            'position': 'relative'
        });
    }
});

HTML

<div class="container">
    <div class="test_content">
        Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus interdum metus nec neque convallis id interdum nibh aliquet. Nulla eget varius diam. Ut ut dolor dolor. Mauris vehicula sodales mi quis euismod. In sem metus, volutpat nec fringilla sed, fermentum ac turpis. Cras aliquam venenatis rutrum. Donec pharetra ante sit amet justo pellentesque nec consequat ante elementum. Ut imperdiet iaculis tortor, id pretium urna pharetra sit amet. Aenean pharetra nunc risus, ac scelerisque urna. Morbi dictum egestas augue, in euismod metus commodo ac. Duis nisl ante, consequat et tincidunt id, eleifend eu ante. Integer lectus velit, tempus eu feugiat et, adipiscing ut mauris.
    </div>

    <!-- This div is used to indicate the original position of the scrollable fixed div. -->
    <div class="scroller_anchor"></div>

    <!-- This div will be displayed as fixed bar at the top of the page, when user scrolls -->
    <div class="scroller">This is the scrollable bar</div>

    <div class="test_content">
        Quisque sollicitudin elit vitae diam consequat accumsan. Suspendisse potenti. Donec dapibus tortor at justo eleifend at pellentesque leo lobortis. Etiam ultrices leo et nulla iaculis eu facilisis augue fermentum. Pellentesque eu leo purus. Vestibulum bibendum, metus at bibendum blandit, lacus neque porttitor diam, id facilisis lectus mauris et leo. Donec adipiscing interdum lacus sed condimentum. In auctor sollicitudin orci, ac interdum risus aliquet ullamcorper. Curabitur mollis accumsan vulputate. Etiam adipiscing diam nec dui posuere ut tincidunt felis tristique. Vestibulum neque enim, placerat sed placerat commodo, consectetur ac mauris. Sed ultrices pretium nibh, a blandit libero imperdiet pulvinar. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae;
    </div>
    ...
</div>

CSS:

.container{font-size:14px; margin:0 auto; width:960px}
.test_content{margin:10px 0;}
.scroller_anchor{height:0px; margin:0; padding:0;}
.scroller{background:#FFF; border:1px solid #CCC; margin:0 0 10px; z-index:100; height:50px; font-size:18px; font-weight:bold; text-align:center; width:960px;}