Develop Reference

Highlighting current section in navbar

I have a scrolling page with a navbar and I want the section the user is scrolling through to be highlighted in the navbar. At the moment it almost accomplishes this, but is highlighting the incorrect link.
A demonstration is at http://codepen.io/meek/pen/NNprYb?editors=1000
The code that does this is as follows:
// highlight current tab
$(window).on("scroll", function() {
var currentPos = $(window).scrollTop();
$('.nav li a').each(function() {
var sectionLink = $(this);
var section = $(sectionLink.attr('href'));
if(section.position().top <= currentPos && sectionLink.offset().top + section.height() >= currentPos) {
$('.nav li').removeClass('active');
sectionLink.parent().addClass('active');
}
else {
sectionLink.parent().removeClass('active');
}
});
});
I've tried several things, but can't get it to reliably add the active class to the correct session. Help appreciated!
edit: to be clearer, the problem is that it's only highlighting the section when you've scrolled a bit into it, instead of right at the top, meaning that when you click a section to scroll to the top of that section automatically, that section is not highlighted.
edit2: So changing the if statement to:
if(currentPos + $('#nav-wrapper').outerHeight() >= section.position().top && currentPos + $('#nav-wrapper').outerHeight() <= sectionLink.offset().top + section.outerHeight()) {
has made an improvement although not completely fixed the issue. The home, about and portfolio sections all highlight the correct link but not contact.

You need to account for the height of the navbar and subtract it from the top of the section you want highlighted.
The height is currently hardcoded in your CSS at 75px but I included a jQuery selector for the height in case it needs to change/disappear for smaller screens.
Nice work by the way.
$(window).on("scroll", function() {
var currentPos = $(window).scrollTop();
$('.nav li a').each(function() {
var sectionLink = $(this);
// capture the height of the navbar
var navHeight = $('#nav-wrapper').outerHeight() + 1;
var section = $(sectionLink.attr('href'));
// subtract the navbar height from the top of the section
if(section.position().top - navHeight <= currentPos && sectionLink.offset().top + section.height()> currentPos) {
$('.nav li').removeClass('active');
sectionLink.parent().addClass('active');
} else {
sectionLink.parent().removeClass('active');
}
});
});

Making nav bar effects using scroll AND click in jQuery

I want a nav to highlight (or something similar) once a user clicks on it AND when a user scrolls to the corresponding section.
However, on my computer when one clicks on any of the nav events after3, only nav event 3 changes. I'm guessing this is because after one clicks on 4 or 5, the scroll bar is already at the bottom of the page, so 4 and 5 never reach the top. The only div at the top is post 3, so my code highlights nav event 3 and ignores the click.
Is there any way I can fix this? Ive tried if statements (only highlight nav event if it's at the top AND the scrollbar isn't at the bottom or the top isn't the last item).
Here is a more accurate fiddle, using a fix below showing what I am talking about. The fix now highlights on scroll, but if you click option 5, it will not highlight.
$('.option').children('a').click(function() {
$('.option').css('background-color', '#CCCCCC;');
$(this).css('background-color', 'red');
var postId = $($(this).attr('href'));
var postLocation = postId.offset().top;
$(window).scrollTop(postLocation);
});
$(window).scroll(function() {
var scrollBar = $(this).scrollTop();
var allPosts = [];
var post = $('.content').offset();
var lastPost = allPosts.legnth-1
var windowHeight = $(window).height();
var bottomScroll = windowHeight-scrollBar;
$(".content").each(function(){
allPosts.push($(this).attr('id'));
});
i = 0;
for(i in allPosts){
var currentPost = "#"+allPosts[i];
var postPosition = $(currentPost).offset().top;
if (scrollBar >= postPosition){
$('.option').css('background-color', '#CCCCCC');
$('#nav'+allPosts[i]).css('background-color', 'red');
};
};
});

I think you've overdone your scroll() handler, to keep it simple you just needs to check if the scrollbar/scrollTop reaches the '.contents' offset top value but should not be greater than its offset().top plus its height().
$(window).scroll(function () {
var scrollBar = $(this).scrollTop();
$(".content").each(function (index) {
var elTop = $(this).offset().top;
var elHeight = $(this).height();
if (scrollBar >= elTop - 5 && scrollBar < elTop + elHeight) {
/* $(this) '.content' is the active on the vewport,
get its index to target the corresponding navigation '.option',
like this - $('.Nav li').eq(index)
*/
}
});
});
And you actually don't need to set $(window).scrollTop(postLocation); because of the default <a> tag anchoring on click, you can omit that one and it will work fine. However if you are looking to animate you need first to prevent this default behavior:
$('.option').children('a').click(function (e) {
e.preventDefault();
var postId = $($(this).attr('href'));
var postLocation = postId.offset().top;
$('html, body').animate({scrollTop:postLocation},'slow');
});
See the demo.

What you are trying to implement from scratch, although commendable, has already been done by the nice folks at Bootstrap. It is called a Scrollspy and all you need to do to implement it is include Bootstrap js and css (you also need jquery but you already have that) and make some minor changes to your html.
Scrollspy implementation steps.
And here is a demonstration. Notice only one line of js. :D
$('body').scrollspy({ target: '.navbar-example' });

jQuery: Using scroll() and offset() to change background

I am designing a website where the background sits in a div that has a negative z-index with position:fixed. I then have section divs that scroll over it. My goal is to change the background image when each section's top position is passed by the scrollTop function. My jQuery code currently creates an array of each sections top position using:
var secTops = [];
$('section').each(function(i) {
var t = $(this).offset();
secTops.push(t.top);
});
I then thought I would create a variable upon scroll() that was the scrollTop() position like so:
$(window).scroll(function() {
var winTop = $(this).scrollTop();
});
But here is where I am stuck. The best I can come up with (which doesn't work right) is this:
for (i = 0; i < $('section').length; i++) {
var pos = secTops[i];
if (winTop < pos) {
$('#background').css('background', bgFront + (i+1) + bgBack);
} else {
$('#background').css('background', bgFront + (i+2) + bgBack);
};
};
But this isn't right. You can disregard the second half of my .css() function. I've created variables and labeled my images appropriately, so i know that works. Right now, the for loop runs through the entire iteration and is stuck at the full section.length and thus only flips between 2 background images. I need this to constantly check my winTop variable against the top positions of my sections and change the background accordingly. I could do this with a lot of if/then, or maybe even a lengthy switch, but there has to be a cleaner way to do this. Can anyone help me out here?
Here's a JSFiddle that uses colors instead of images but shows the same problems. http://jsfiddle.net/kyleshevlin/5N5WU/1/

this has no chance to work. you need to change it to something like this (this is kinda pseudocode, just to give you a picture:
sections = [];
$(document).ready(function() {
$('section').each(function() {
sections.push($(this))
});
})
$(window).scroll(function() {
var s = $(window).scrolTop();
var currentIndex;
for ( var i = 0; i < sections.length; i++) {
if (( s > sections[i].offset().top) && ( s <= sections[i+1].offset().top)) {
currentIndex = i;
}
}
$('#background').css('background', bgFront + (i+1) + bgBack);
})

Change url when manually scrolled to an anchor?

By Default, if I have anchors in my website, then the URL on the address bar is changed, when I click on a link (ie. www.mysite.com/#anchor)
Is it possible to change the URL in the address bar instantly when I scroll to an anchor? Or have a long document with multiple anchors and the url changes on address bar, when I hit a new anchor?

Try using this jquery plugin: Scrollorama. It has tons of cool features and you can use window.location.hash to update your browsers hash.
Alternatively, you can add a "scroll" event to check when an anchor is reached.
Here is a working fiddle to illustrate the event: http://jsfiddle.net/gugahoi/2ZjWP/8/
Example:
$(function () {
var currentHash = "#initial_hash"
$(document).scroll(function () {
$('.anchor_tags').each(function () {
var top = window.pageYOffset;
var distance = top - $(this).offset().top;
var hash = $(this).attr('href');
// 30 is an arbitrary padding choice,
// if you want a precise check then use distance===0
if (distance < 30 && distance > -30 && currentHash != hash) {
window.location.hash = (hash);
currentHash = hash;
}
});
});
});

you can use HTML 5 pushstate to change the URL in the address bar
window.history.pushstate
https://developer.mozilla.org/en-US/docs/DOM/Manipulating_the_browser_history
How can I use window.history.pushState 'safely'

Bind a handler to jquery scroll event.
Check if an anchor is currently visible on-screen with this jquery
script.
Use pushstate or set location (probably will cause jumps)

You can bind to the jQuery scroll event (http://api.jquery.com/scroll/) and on each call of the callback called, check how far on the document the user has scrolled by checking this value: .scrollTop (http://api.jquery.com/scrollTop/) and set the anchor by manipulating te location.hash object (http://www.w3schools.com/jsref/prop_loc_hash.asp).
It would be something like this:
// Checks if the passed element is visible on the screen after scrolling
// source: http://stackoverflow.com/questions/487073/check-if-element-is-visible-after-scrolling
function isScrolledIntoView(elem) {
var docViewTop = $(window).scrollTop();
var docViewBottom = docViewTop + $(window).height();
var elemTop = $(elem).offset().top;
var elemBottom = elemTop + $(elem).height();
return ((elemBottom <= docViewBottom) && (elemTop >= docViewTop));
}
$('#document').scroll(function(e) {
var anchors = $('.anchor');
for (var i = 0; i < anchors.length; ++i) {
if (isScrolledIntoView(anchors[i])){
var href = $(anchors[i]).attr('href');
location.hash = href.slice(href.indexOf('#') + 1);
break;
}
}
});
You could be more precise, if you sort the anchors after selecting them, so that the first visible anchor will be set always.

Plain js version
While researching how to update the URL based off positions of HTML section elements on the screen, I kept finding this thread so I hope this is a good place to post this.
This function loops over the HTML section elements.
function updateFragId() {
var len = sections.length;
for (var i = 0; i < len; i++) {
var id = sections[i].id;
Collects the Y scroll position relative to the viewport.
var rect = sections[i].getBoundingClientRect().y;
convert the two arrays into an object
var pageData = {id:id, rect:rect};
set a range for the code to trigger in between. Here it will trigger when the top of the section element is between -200px to 400px
if (pageData.rect > -200 && pageData.rect < 400) {
only run once by making sure the pageData.id and location.hash dont already match. This stops it from flooding your browser with events.
if (pageData.rect > -100 && pageData.rect < 100) {
if (pageData.id !== location.hash.substr(1)) {
fragmentId = pageData.id;
setActiveLink(fragmentId);
} else {
return;
}
}
}
}
window.addEventListener('scroll', updateFragId);
I use a debouncer on this block of code with another block to set the active link. But this is just how to track the # anchors.

I think you need to do something like this. Not tried in action
var myElements = $("div.anchor"); // You target anchors
$(window).scroll(function(e) {
var scrollTop = $(window).scrollTop();
myElements.each(function(el,i) {
if ($(this).offset().top > scrollTop && $(myElements[i+1]).offset().top < scrollTop) {
location.hash = this.id;
}
});
});

Getting Coordinates of an element on page scroll

I am having this problem where i have a set of 6 UL's having a common class x.Each of them consist of a specific section of the page.Now i have 6 menus that are related to each of the section.What i have to do is highlight the menu when its related section is in users view.
For this i thought that may be jQuery position(); or offset(); could have helped but they give the top and left of the element.I also tried using jQuery viewport plugin but apparently view port is big it can show more than one UL at a time hence i cant apply element specific logic here.I am not familliar to this but does anything changes of an element on scrolling?If yes then how to access it?
Please share your views.
Regards
Himanshu Sharma.

Is very easy to do it using jQuery and a dummy fixed HTML block that helps you find the current position of the viewport.
$(window).on("scroll load",function(){
var once = true;
$(".title").each(function(ele, index){
if($(this).offset().top > $("#viewport_helper").offset().top && once){
var index = $(this).index(".title");
$(".current").removeClass('current')
$("#menu li").eq(index).addClass('current')
once = false;
}
});
})
Check out a working example: http://jsfiddle.net/6c8Az/1/
You could also do something similar with the jQuery plugin, together with the :first selector:
$(window).on("scroll load",function(){
$(".title:in-viewport:first").each(function(){
var index = $(this).index(".title");
$(".current").removeClass('current')
$("#menu li").eq(index).addClass('current')
});
})

You can get the viewport's width and height via $(document).width() and $(document).height()
You can get how many pixels user scrolls via $(document).scrollTop() and $(document).scrollLeft
Combining 1 and 2, you can calculate where the viewport rectangle is
You can get the rectangle of an element using $(element).offset(), $(element).width() and $(element).height()
So the only thing left to you is to determine whether the viewport's rectangle contains (or interacts) the elements's rectangle
So the whole code may look like:
/**
* Check wether outer contains inner
* You can change this logic to matches what you need
*/
function rectContains(outer, inner) {
return outer.top <= inner.top &&
outer.bottom >= inner.bottom &&
outer.left <= inner.left &&
outer.right >= inner.right;
}
/**
* Use this function to find the menu related to <ul> element
*/
function findRelatedMenu(element) {
return $('#menu-' + element.attr('id'));
}
function whenScroll() {
var doc = $(document);
var elem = $(element);
var viewportRect = {
top: doc.scrollTop(),
left: doc.scrollLeft(),
width: doc.width(),
height: doc.height()
};
viewportRect.bottom = viewportRect.top + viewportRect.height;
viewportRect.right = viewportRect.left + viewportRect.width;
var elements = $('ul.your-class');
for (var i = 0; i < elements.length; i++) {
var elem = $(elements[i]);
var elementRect = {
top: elem.offset().top,
left: elem.offset().left,
width: elem.width(),
height: elem.height()
};
elementRect.bottom = elementRect.top + elementRect.height;
elementRect.right = elementRect.left + elementRect.width;
if (rectContains(viewportRect, elementRect)) {
findRelatedMenu(elem).addClass('highlight');
}
}
}
$(window).on('scroll', whenScroll);

Let's see if i understood well. You have a page long enough to scroll, and there is an element that when it appears in the viewport, you wanna do something with it. So the only event that's is triggered for sure on the time the element gets in the viewport is the 'scroll'. So if the element is on the page and the scroll is on the viewport, what you need to do is bind an action to the scroll event to check if the element is in the view each time the event is trigger. Pretty much like this:
$(window).scroll(function() {
check_element_position();
});
Now, in order for you to know if the element is in the viewport, you need 3 things. The offset top of that element, the size of the viewport and the scroll top of the window. Should pretty much look like this:
function check_element_position() {
var win = $(window);
var window_height = win.height();
var element = $(your_element);
var elem_offset_top = element.offset().top;
var elem_height = element.height();
var win_scroll = win.scrollTop();
var pseudo_offset = (elem_offset_top - win_scroll);
if (pseudo_offset < window_height && pseudo_offset >= 0) {
// element in view
}
else {
// elem not in view
}
}
Here, (elem_offset_top - win_scroll) represent the element position if there was no scroll. Like this, you just have to check if the element offset top is higher then the window viewport to see if it's in view or not.
Finally, you could be more precise on you calculations by adding the element height (variable already in there) because the code i just did will fire the event even if the element is visible by only 1 pixels.
Note: I just did that in five minutes so you might have to fix some of this, but this gives you a pretty darn good idea of what's going on ;)
Feel free to comment and ask questions