Develop Reference

JavaScript Focus() on Element ID with Floating Navigation Bar?

On form validation, to prompt the user to fill out the required fields.
The usual;
document.getElementById("idHere").focus();
When dealing with floating navigation bars at the top of the screen, this doesn't always work, mainly when the element you want to focus on is the first one, it hides behind the floating navigation.
Is there a handy solution to nudge the Focus down a set number of pixels to make sure this takes into account the size of the navigation menu?

You must add a scroll function to your function or the element onFocus.
it could be like this :
window.scrollTo( window.scrollX , document.getElementById("idHere").scrollTop + 80 );

Here is the solution as a jQuery function. You use it by passing a selector by whatever elements you want to have the behavior. For example bindFocusScroll('input, select');
function bindFocusScroll(selector){
var navHeight = 192;
var padding = 25;
$(selector).on('focus', function() {
try {
var elemTop = $(this).offset().top;
var maxVisible = $(document).scrollTop() + navHeight;
if (elemTop < maxVisible) {
$("html, body").animate({ scrollTop: elemTop - navHeight - padding }, 250);
}
} catch (e) {
console.log("Error: " + e);
}
});
}
If you don't need it to animate or be smart you can just use Sasan's answer. I can help you recreate this answer in vanilla JS if needed as well.

jQuery scroll event: how to determine amount scrolled (scroll delta) in pixels?

I have this event:
$(window).scroll(function(e){
console.log(e);
})
I want to know, how much I have scroll value in pixels, because I think, scroll value depends from window size and screen resolution.
Function parameter e does not contains this information.
I can store $(window).scrollTop() after every scroll and calculate difference, but can I do it differently?

The "scroll value" does not depend on the window size or screen resolution. The "scroll value" is simply the number of pixels scrolled.
However, whether you are able to scroll at all, and the amount you can scroll is based on available real estate for the container and the dimensions of the content within the container (in this case the container is document.documentElement, or document.body for older browsers).
You are correct that the scroll event does not contain this information. It does not provide a delta property to indicate the number of pixels scrolled. This is true for the native scroll event and the jQuery scroll event. This seems like it would be a useful feature to have, similar to how mousewheel events provide properties for X and Y delta.
I do not know, and will not speculate upon, why the powers-that-be did not provide a delta property for scroll, but that is out of scope for this question (feel free to post a separate question about this).
The method you are using of storing scrollTop in a variable and comparing it to the current scrollTop is the best (and only) method I have found. However, you can simplify this a bit by extending jQuery to provide a new custom event, per this article: http://learn.jquery.com/events/event-extensions/
Here is an example extension I created that works with window / document scrolling. It is a custom event called scrolldelta that automatically tracks the X and Y delta (as scrollLeftDelta and scrollTopDelta, respectively). I have not tried it with other elements; leaving this as exercise for the reader. This works in currrent versions of Chrome and Firefox. It uses the trick for getting the sum of document.documentElement.scrollTop and document.body.scrollTop to handle the bug where Chrome updates body.scrollTop instead of documentElement.scrollTop (IE and FF update documentElement.scrollTop; see https://code.google.com/p/chromium/issues/detail?id=2891).
JSFiddle demo: http://jsfiddle.net/tew9zxc1/
Runnable Snippet (scroll down and click Run code snippet):
// custom 'scrolldelta' event extends 'scroll' event
jQuery.event.special.scrolldelta = {
delegateType: "scroll",
bindType: "scroll",
handle: function (event) {
var handleObj = event.handleObj;
var targetData = jQuery.data(event.target);
var ret = null;
var elem = event.target;
var isDoc = elem === document;
var oldTop = targetData.top || 0;
var oldLeft = targetData.left || 0;
targetData.top = isDoc ? elem.documentElement.scrollTop + elem.body.scrollTop : elem.scrollTop;
targetData.left = isDoc ? elem.documentElement.scrollLeft + elem.body.scrollLeft : elem.scrollLeft;
event.scrollTopDelta = targetData.top - oldTop;
event.scrollTop = targetData.top;
event.scrollLeftDelta = targetData.left - oldLeft;
event.scrollLeft = targetData.left;
event.type = handleObj.origType;
ret = handleObj.handler.apply(this, arguments);
event.type = handleObj.type;
return ret;
}
};
// bind to custom 'scrolldelta' event
$(window).on('scrolldelta', function (e) {
var top = e.scrollTop;
var topDelta = e.scrollTopDelta;
var left = e.scrollLeft;
var leftDelta = e.scrollLeftDelta;
// do stuff with the above info; for now just display it to user
var feedbackText = 'scrollTop: ' + top.toString() + 'px (' + (topDelta >= 0 ? '+' : '') + topDelta.toString() + 'px), scrollLeft: ' + left.toString() + 'px (' + (leftDelta >= 0 ? '+' : '') + leftDelta.toString() + 'px)';
document.getElementById('feedback').innerHTML = feedbackText;
});
#content {
/* make window tall enough for vertical scroll */
height: 2000px;
/* make window wide enough for horizontal scroll */
width: 2000px;
/* visualization of scrollable content */
background-color: blue;
}
#feedback {
border:2px solid red;
padding: 4px;
color: black;
position: fixed;
top: 0;
height: 20px;
background-color: #fff;
font-family:'Segoe UI', 'Arial';
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id='feedback'>scrollTop: 0px, scrollLeft: 0px</div>
<div id='content'></div>
Note that you may want debounce the event depending on what you are doing. You didn't provide very much context in your question, but if you give a better example of what you are actually using this info for we can provide a better answer. (Please show more of your code, and how you are using the "scroll value").

To detemine how many pixels were scrolled you have to keep in mind that the scroll event gets fired almost every pixel that you move. The way to accomplish it is to save the previous scrolled value and compare that in a timeout. Like this:
var scrollValue = 0;
var scrollTimeout = false
$(window).scroll(function(event){
/* Clear it so the function only triggers when scroll events have stopped firing*/
clearTimeout(scrollTimeout);
/* Set it so it fires after a second, but gets cleared after a new triggered event*/
scrollTimeout = setTimeout(function(){
var scrolled = $(document).scrollTop() - scrollValue;
scrollValue = $(document).scrollTop();
alert("The value scrolled was " + scrolled);
}, 1000);
});
This way you will get the amount of scrolled a second after scrolling (this is adjustable but you have to keep in mind that the smooth scrolling that is so prevalent today has some run-out time and you dont want to trigger before a full stop).

The other way to do this? Yes, possible, with jQuery Mobile
I do not appreciate this solution, because it is necessary to include heavy jQuery mobile. Solution:
var diff, top = 0;
$(document).on("scrollstart",function () {
// event fired when scrolling is started
top = $(window).scrollTop();
});
$(document).on("scrollstop",function () {
// event fired when scrolling is stopped
diff = Math.abs($(window).scrollTop() - top);
});

To reduce the used processing power by adding a timer to a Jquery scroll method is probably not a great idea. The visual effect is indeed quite bad.
The whole web browsing experience could be made much better by hiding the scrolling element just when the scroll begins and making it slide in (at the right position) some time after. The scrolling even can be checked with a delay too.
This solution works great.
$(document).ready(function() {
var element = $('.movable_div'),
originalY = element.offset().top;
element.css('position', 'relative');
$(window).on('scroll', function(event) {
var scrollTop = $(window).scrollTop();
element.hide();
element.stop(false, false).animate({
top: scrollTop < originalY
? 0
: scrollTop - originalY + 35
}, 2000,function(){element.slideDown(500,"swing");});
});
});
Live demo here

Jquery when the user hits bottom of the page

I've been working on a scroll to top function for my website, and that part of it works fine. My problem is however that I have a fixed div that is overlapping my footer when it hits the bottom of the page.
Here is the function that I have working.
$(document).scroll(function (e) {
if (document.body.scrollTop >= 800) {
$('#beamUp').show(1000);
} else {
$('#beamUp').hide(1000);
return false;
}
});
Is there somehow I could detect when I hit that part of the page and stop the div from moving past that.Help is much appreciated!
jsFiddle: http://jsfiddle.net/zazvorniki/RTDpw/

Just get the height of the page, minus the height of the div in question, as well as the footer... make sure the top is never greater than that value... you'll also need an onresize event handler re-evaluate that value.
looking at your jsfiddle... here are my edits
In your scroll listener, I am checking for the position of the page, and adjusting the bottom position of the floater appropriately. I also set the initial display:none, so you don't need to call .hide() in your initial script. In addition, resizing the window has the effect of scrolling for your use, so I changed the listener for both events.
$(document).on('scroll resize', function (e) {
var viewHeight = $(window).height();
var viewTop = $(window).scrollTop();
var footerTop = $("footer").offset().top;
var baseline = (viewHeight + viewTop) - footerTop;
var bu = $("#beamUp").css({bottom: (baseline < 0 ? 0 : baseline) + 'px'});
if (viewTop >= 50) {
bu.show(1000);
} else {
bu.hide(1000);
}
});

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

Determine whether mouse is always on the bottom of the page

How can I determine whether mouse is always on the bottom of the viewport? Let us assume that by bottom we mean the bottom 100 pixels of a given page (on a long scrolling page).
this is an example, check the arrow
http://discover.store.sony.com/tablet/#design/weight-distribution

Easy!
Calculate how much of that "bottom" area is showing in the current window with window.screen.height and document.height.
Then use onmousemove event to calculate if the mouse is stepping over that area.

Create a blank div with the dimensions that you want, use CSS to position:absolute; it on the bottom and z-index it above the other elements, then create a onHover to detect if the mouse is there
EDIT
This might work as a solution to avoid using CSS method above (untested)
$(function(){
$.mousemove(function(e){
var wHeight = $(window).height();
var yMouse = e.pageY;
if(yMouse > (wHeight - 100)) {
// Do something
}
});
});

I think i solved myself based on Pastor Bones code:
you have to calculate the window scrolltop
var scrollT = $(window).scrollTop() + wHeight;
so:
$(function(){
$.mousemove(function(e){
var wHeight = $(window).height();
var scrollT = $(window).scrollTop() + wHeight;
var yMouse = e.pageY;
if(yMouse > (scrollT - 100)) {
// Do something
}
});
});