Develop Reference

Prevent viewport from moving when removing DOM elements

I'm trying to implement an HTML infinite scroller in which at any given time there are only a handful of div elements on list (to keep the memory footprint small).
I append a new div element to the list and at the same time I'm removing the first one, so the total count of divs remains the same.
Unfortunately the viewport doesn't stay still but instead it jumps backwards a little bit (the height of the removed div actually).
Is there a way to keep the viewport still while removing divs from the list?
I made a small self contained HTML page (well, it still needs JQuery 3.4.1) which exposes the problem: it starts by adding 5 divs and then it keeps adding a new one and removing the first one every 1 second
function getRandomColor() {
var letters = '0123456789ABCDEF';
var color = '#';
for (var i = 0; i < 6; i++) {
color += letters[Math.floor(Math.random() * 16)];
}
return color;
}
function removeit() {
// remove first one
var tiles = $(".tile");
$(tiles[0]).remove();
}
function addit() {
// append new one
var jqueryTextElem = $('<div class="tile" style="height:100px;background-color:' + getRandomColor() + '"></div>');
$("#inner-wrap").append(jqueryTextElem);
}
function loop() {
removeit();
addit();
window.setTimeout(loop, 1000);
}
addit();
addit();
addit();
addit();
addit();
loop();
<div id="inner-wrap"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>

You can temporarily add position: fixed to the parent element:
first add position: fixed to the parent;
then remove the item;
then remove position: fixed from the parent

I have a feeling you're trying to have your cake and eat it, in that if you get the viewport to be "still", I think you're meaning you don't want a user to see the scrollbar move and then also not have any new affordance to scroll further down the page, because you would want the scrollbar thumb/grabber to still sit at the bottom of the scrollbar track?
I mean, you could just use $(window).scrollTop($(window).scrollTop() + 100); in your example to make it so the scroll position of the viewport won't visually move when removing elements, but at that point, you wouldn't be keeping the users view of the current elements the same or even allowing a user to have new content further down the page to scroll towards. You'd just be "pushing up" content through the view of the user?
If you are trying to lighten the load of what is currently parsed into document because you are doing some heavy lifting on the document object at runtime, maybe you still want to remove earlier elements, but retain their geometry with some empty sentinel element that always has the height of all previously removed elements added to it? This would allow you to both have a somewhat smaller footprint (though not layout-wise), while still having a usable scrollbar that can communicate to a user and both allow a user to scroll down, towards the content that has been added in.
All in all, I think what you currently have is how most infinite scrollers do and should work, meaning the scroll position and scrollbar should change when content is added in the direction the user is scrolling towards, this communicates to them that they can in fact keep scrolling that way. You really shouldn't want the viewports scroll position to be "still".
To see more clearly why I don't think you have an actual issue, replace your loop() definition with something like this...
function loop() {
$(window).scroll(function() {
// check for reaching bottom of scroller
if ($(window).scrollTop() == ($(document).height() - $(window).height())) {
addit();
removeit();
}
})
}

Setting up max-height and not overflow

Some background: I have a div in which elements of different height will be added to and I'm in need of achieving the following:
The div has a max-height property, when the different elements that are added to the Div overlap such height, I can't have the div "overflowing (putting a scrollbar on it)". Instead, I need to detect when this happens, so I can create ANOTHER div in which I could put the rest of the elements. Attached is an image that I hope illustrates what I'm trying to do.

Use jQuery:
var maxHeight = $(".someElement").css("max-height");
var height = 0;
$(".elements").each(function(){
height += $(this).height();
if(height >= maxHeight){
//create new div here and put the rest of the elements there
height = 0; //so you can continue with the loop and creating more divs.
}
});

I have a pseudo function below that I think could get you started on the right track. You will have to fill in the appropriate information for it.
$(elements).each(function() {
var currentDiv = $(currentDiv);
if($(currentDiv ).height() > MAX_HEIGHT)
{
$(currentDiv).insertAfter(newDiv);
currentDiv = $(newDiv);
}
$(currentDiv).append(element);
});
You'll have to keep track of the current div you are adding info to. Just add info like normal but when it overflows you should insertAfter it a new div and change the current div variable to be that one and then continue appending again.

To test if a div is currently overflowing, compare it's scrollHeight to its height.
With jQuery
if ($(obj)[0].scrollHeight > $(obj).height()) {
// do stuff
}
In this case though, you'll probably want to test against the css max-height before adding content. To do this (again in jQuery) load the content you plan to add into a variable so you can check its height before adding it to the document.
var content = // your content here
if ($(container).height() + content.height() > parseInt($(container).css("max-height"), 10)) {
// this means it would overflow, so do stuff
} else {
// no overflow here
$(container).append(content);
}
Here's a quick fiddle. http://jsfiddle.net/k0g47xdr/2/
edit:
the parseInt call around .css("max-height") is to convert from the text format it comes in to a regular number. As written it assumes the value is in px, not em or percent.

Javascript Arranging Images as Pile of Cards

Im new to javascript so im sure there is a lot i am missing in its understanding.
What i am trying to do it create a layer of images so that it looks like a pile of cards.
have seen similar codes and have tried to follow their idea but i just cant get the images to position properly. All 10 or so images are place in the exact same location.
Can any help to see why they not positioning? Also what is "em". I cant find any literature on it but assume it is the measurement em like px ?? Why is it in "" ?
function Display() {
var el;
var left = 0;
var top = 0;
var i=0;
var n = deck.length;
var cardNode;
var img = document.createElement("IMG");
img.src = "wendell7_back.png";
el = document.getElementById('deck');
el.appendChild(img);
while (el.firstChild != null) el.removeChild(el.firstChild);
for (i = 0; i < Math.round(n / 5); i++)
{
cardNode = document.createElement("DIV");
cardNode.appendChild(img);
cardNode.style.left = left + "em";
cardNode.style.top = top + "em";
el.appendChild(cardNode);
left += 0.1;
top += 0.1;
}
}

"em" is the width of an "M" in whichever font is being used (or browser's default font if nothing overrides it).
There are at least two things wrong in your code:
left and top have no meaning unless the element to which they are applied also has position:absolute or position:relative (or position:fixed I think). Your safest approach is to apply position:relative (but no left: or top:) to the container and position:absolute to each of the cards.
There's only one img. For multiple cards, you need multiple imgs otherwise the same img gets repositioned over and over.
A more economical approach is probably to show a separate "stack" image for multiple cards and single card images for a single cards.
An even more economical approach is only to show single card images with a "tooltip" to indicate the number of cards in a stack. I have successfully employed this technique in an implementation of a game of patients.
Of course, these alternative techniques don't work if you want to show multiple cards as a "fanned out" stack of upturned cards.
Create a class and modify the position of that for the deck. Here is the working code:
function Display() {
var el;
var left = 0;
var top = 0;
var i=0;
var n = deck.length;
var cardNode;
el = document.getElementById('deck');
while (el.firstChild != null) el.removeChild(el.firstChild);
for (i = 0; i < Math.round(n / 5); i++)
{
cardNode = document.createElement("DIV");
cardNode.className = "card2";
var img = document.createElement("IMG");
img.src = "wendell7_back.png";
cardNode.appendChild(img);
cardNode.style.left = left + "em";
cardNode.style.top = top + "em";
el.appendChild(cardNode);
left += .1;
top -= 6.2;
}
}
Hope this will help.

There are a couple of problems with that code.
You're only using one img, and then you're appending it to each div you create. When you append an element to another element, if it's already in the DOM tree, you end up moving it. What you need is to create a separate img element for each card.
You haven't shown us your CSS, but unless you're using CSS to make all div elements under the #deck element absolutely or relatively positioned, the left and top style attributes will be ignored, as the div will be subject to normal flow.
Also what is "em". I cant find any literature on it but assume it is the measurement em like px ??
Yes, it's a term from typography. An "em" is the width of a capital letter M.
Why is it in "" ?
Because it's a string. You'd also have to have "px" in quotes. What you're doing with this code:
cardNode.style.left = left + "em";
...is using JavaScript to set a style property. Style properties are always strings, in this case you're creating strings like "0.1em" and "0.2em", etc.
Some reading:
DOM2 Core specification
DOM2 HTML specification
DOM3 Core specification
HTML5 specification
Various CSS specifications
A good book on JavaScript, I quite liked JavaScript: The Definitive Guide by David Flanagan
A good book on CSS and HTML authoring

My guess is that your offset is too small: if you replace the "em" with "px" for test's sake, and increase the left and top variables by 10 instead of 0.1, I bet you'll see some results.
To explain the em: 1em is equal to the current font-size of the element. If you haven't set the font size it uses the browser default. If you set the font-size to be e.g. 20px on the body tag, then 1em will equal 20px.

Make sure that your 'cards' have the css property 'position' set - either to 'absolute' or 'relative'.

issue with $(document).scrollLeft() as a variable

I'm trying to use the left variable to replace '1493' in this code. It works fine when it's a number but when I changed it over to use 'left' the if statement stops working.
$(document).scroll(function () {
var width = $(document).width();
var left = $(document).scrollLeft();
var postCount = $(".post").length;
var columnLength = ( width - ((postCount*743) - 1493)) - (width-(postCount*743));
if(left >= columnLength) {
$(".num").text(left);
}
});
Does anyone have any ideas where I'm going wrong with this? Any pointers would be great.

You may need to force it to be an integer:
var left = parseInt($(document).scrollLeft());

Lets take a look at the math you have really quick.
var columnLength = ( width - ((postCount*743) - 1493)) - (width-(postCount*743));
You are basically cancelling out width, and (postCount*743). It leaves you with --1493 which is positive 1493. The following would have the same effect:
var columnLength = 1493;
So, the reason the if statement fires when you put in the static value 1493, is because columnLength ALWAYS equals 1493 which, of course satisfies this condition:
if (1493 >= columnLength)
You could as easily write:
if (1493 >= 1493)
That said, it should still, theoretically fire when left becomes greater than or equal to 1493. But left is the current horizontal scroll position in pixels. It would be a HUGELY wide page to hit a scroll position of 1493.
Edit: Here's a fiddle to give an idea of how fast the scroll position increases: http://jsfiddle.net/vdQ7B/16/
EDIT 2:
Here is an update in response to your comment.
As I understand it, you were trying to get a horizontal scrollbar that would, essentially, scroll forever.
Please see the following fiddle for a demo: http://jsfiddle.net/vdQ7B/40/
The code is below:
$(document).scroll(function () {
var width = $(document).width();
var left = $(document).scrollLeft();
var viewportwidth = window.innerWidth;
// If our scrollbar gets to the end,
// add 50 more pixels. This could be set
// to anything.
if((left + viewportwidth) === width) {
$("body").css("width", width + 50);
}
});
Per the comments in the code, we simply increase the width of the body if we determine we've reached the end. scrollLeft() will only tell us the number of pixels that are currently not visible to the left of the viewable area. So, we need to know how much viewable area we have, and how much is hidden to the left to know if we've scrolled all the way to the end.
If you have a scroll bar on an inner element, like a div, you'd need to update with width of the div, not the body.
Note: You may also need to use $(window) instead of $(document) to get scrollLeft() to work across all browsers.
Note: See here about using "innerWidth". There are some compatibility issues, and you may need to expand it a bit to handle other cases (IE6).

Jquery - Truncate Text by Line (not by character count)

I need a Jquery script to truncate a text paragraph by line (not by character count).
I would like to achieve an evenly truncated text-block. It should have a "more" and "less" link to expand and shorten the text paragraph. My text paragraph is wrapped in a div with a class, like this:
<div class="content">
<h2>Headline</h2>
<p>The paragraph Text here</p>
</div>
The closest solution i could find on SOF is the one below (but it`s for textarea element and does not work for me):
Limiting number of lines in textarea
Many thanks for any tips.
Ben

For a basic approach, you could take a look at the line-height CSS property and use that in your calculations. Bear in mind that this approach will not account for other inline elements that are larger than that height (e.g. images).
If you want something a bit more advanced, you can get the information about each line using getClientRects() function. This function returns a collection of TextRectangle objects with width, height and offset for each one.
See this answer here for an example (albeit an unrelated goal) of how getClientRects() works.
Update, had a bit of time to come back and update this answer with an actual example. It's basic, but you get the idea:
http://jsbin.com/ukaqu3/2
A couple of pointers:
The collection returned by getClientRects is static, it won't update automatically if the containing element's dimensions change. My example works around this by capturing the window's resize event.
For some strange standards-compliance reason that I'm not understanding, the element you call getClientRects on must be an inline element. In the example I have, I use a container div with the text in another div inside with display: inline.

I made this little jQuery code to allow me truncate text blocks by line (via CSS classes), feel free to use and comment it.
Here is the jsFiddle, which also include truncate functions by char count or word count. You can see that currently, resize the window won't refresh the block display, I'm working on it.
/*
* Truncate a text bloc after x lines
* <p class="t_truncate_l_2">Lorem ipsum magna eiusmod sit labore.</p>
*/
$("*").filter(function () {
return /t_truncate_l_/.test($(this).attr('class'));
}).each(function() {
var el = $(this);
var content = el.text();
var classList = el.attr('class').split(/\s+/);
$.each(classList, function(index, item){
if(/^t_truncate_l_/.test(item)) {
var n = item.substr(13);
var lineHeight = parseInt(el.css('line-height'));
if(lineHeight == 1 || el.css('line-height') == 'normal')
lineHeight = parseInt(el.css('font-size')) * 1.3;
var maxHeight = n * lineHeight;
var truncated = $.trim(content);
var old;
if(el.height() > maxHeight)
truncated += '...';
while(el.height() > maxHeight && old != truncated) {
old = truncated;
truncated = truncated.replace(/\s[^\s]*\.\.\.$/, '...');
el.text(truncated);
}
}
});
});

why not make the p element with overflow: hidden; give fixed line height, caluclate the height of the div so id contains exactly the number of lines you require and the only change the height of the p from javascript.
p{
overflow:hidden;
line-height:13px;
height:26px; /* show only 2 rows */
}
<script type="text/javascript">
function seeMoreRows(){
$(p).height("52px");
}
</script>

I made a small module that works with pure text content, no nested tags and no css-padding on the text-containing element is allowed (but this functionality could easily be added).
The HTML:
<p class="ellipsis" data-ellipsis-max-line-count="3">
Put some multiline text here
</p>
The Javascript/Jquery:
( function() {
$(document).ready(function(){
store_contents();
lazy_update(1000);
});
// Lazy update saves performance for other tasks...
var lazy_update = function(delay) {
window.lazy_update_timeout = setTimeout(function(){
update_ellipsis();
$(window).one('resize', function() {
lazy_update(delay);
});
}, delay);
}
var store_contents = function(){
$('.ellipsis').each(function(){
var p = $(this);
p.data('ellipsis-storage', p.html());
});
}
var update_ellipsis = function(){
$('.ellipsis').each(function(){
var p = $(this);
var max_line_count = p.data('ellipsis-max-line-count');
var line_height = p.html('&nbsp').outerHeight();
var max_height = max_line_count*line_height;
p.html(p.data('ellipsis-storage'));
var p_height = p.outerHeight();
while(p_height > max_height){
var content_arr = p.html().split(' ');
content_arr.pop();
content_arr.pop();
content_arr.push('...');
p.html(content_arr.join(' '));
p_height = p.outerHeight();
}
});
}
} )();
I hope you like it!

If you used a monospaced font, you'd have a shot at this working, as you'd have a good idea how many letters fit onto each line, for an element of a defined width. However, if a word breaks across lines, then this might get tricky..
e: found another question which is basically what you're after - they didn't really have a resolution either, but to my mind, the line-height and element height seems closest.
"How can I count text lines inside a dom element"

tl;dr - set a height on your container div and then use the jQuery dotdotdot plugin
Was about to make #Andy E's awesome example into a plugin, but then realized https://github.com/BeSite/jQuery.dotdotdot could pull this off. Our use case is we want to show one line on desktop widths and two lines on mobile/tablet.
Our CSS will just set the container div to the equivalent of one or two line-height's accordingly and then the dotdotdot plugin appears to handle the rest.