Updating the DOM based on scroll position with Twitter Bootstrap? - dom

Question

If you look at this page: http://twitter.github.com/bootstrap/components.html
Note the submenu and it's position. Now scroll down - notice how it changes? I assumed they implemented it with the scrollspy plugin but I can't seem to figure out how to do it, all I can do is update which list element has the active class.
Any help would be much appreciated :)

Answer 1

You can find this bit of code in the application.js file, it doesn't look as though it's included in the download. It's available here...funnily enough the header comment reads
// NOTICE!! DO NOT USE ANY OF THIS JAVASCRIPT
// IT'S ALL JUST JUNK FOR OUR DOCS!
// ++++++++++++++++++++++++++++++++++++++++++
This is the part that does the heavy lifting I believe...haven't tested it, just stepped through the code in Chrome
// fix sub nav on scroll
var $win = $(window)
, $nav = $('.subnav')
, navTop = $('.subnav').length && $('.subnav').offset().top - 40
, isFixed = 0
processScroll()
$win.on('scroll', processScroll)
function processScroll() {
var i, scrollTop = $win.scrollTop()
if (scrollTop >= navTop && !isFixed) {
isFixed = 1
$nav.addClass('subnav-fixed')
} else if (scrollTop <= navTop && isFixed) {
isFixed = 0
$nav.removeClass('subnav-fixed')
}
}

Answer 2

CCBlackburn's answer is close though its missing the required stylesheet. For posterity I've also included the javascript. Anyway I got it working using the following:
Javascript
// fix sub nav on scroll
var $win = $(window)
, $nav = $('.subnav')
, navTop = $('.subnav').length && $('.subnav').offset().top - 40
, isFixed = 0
processScroll()
// hack sad times - holdover until rewrite for 2.1
$nav.on('click', function () {
if (!isFixed) setTimeout(function () { $win.scrollTop($win.scrollTop() - 47) }, 10)
})
$win.on('scroll', processScroll)
function processScroll() {
var i, scrollTop = $win.scrollTop()
if (scrollTop >= navTop && !isFixed) {
isFixed = 1
$nav.addClass('subnav-fixed')
} else if (scrollTop <= navTop && isFixed) {
isFixed = 0
$nav.removeClass('subnav-fixed')
}
}
Stylesheet
/* Fixed subnav on scroll, but only for 980px and up (sorry IE!) */
#media (min-width: 980px) {
.subnav-fixed {
position: fixed;
top: 40px;
left: 0;
right: 0;
z-index: 1020; /* 10 less than .navbar-fixed to prevent any overlap */
border-color: #d5d5d5;
border-width: 0 0 1px; /* drop the border on the fixed edges */
-webkit-border-radius: 0;
-moz-border-radius: 0;
border-radius: 0;
-webkit-box-shadow: inset 0 1px 0 #fff, 0 1px 5px rgba(0,0,0,.1);
-moz-box-shadow: inset 0 1px 0 #fff, 0 1px 5px rgba(0,0,0,.1);
box-shadow: inset 0 1px 0 #fff, 0 1px 5px rgba(0,0,0,.1);
filter: progid:DXImageTransform.Microsoft.gradient(enabled=false); /* IE6-9 */
}
.subnav-fixed .nav {
width: 938px;
margin: 0 auto;
padding: 0 1px;
}
.subnav .nav > li:first-child > a,
.subnav .nav > li:first-child > a:hover {
-webkit-border-radius: 0;
-moz-border-radius: 0;
border-radius: 0;
}
}
/* LARGE DESKTOP SCREENS */
#media (min-width: 1210px) {
/* Update subnav container */
.subnav-fixed .nav {
width: 1168px; /* 2px less to account for left/right borders being removed when in fixed mode */
}
}