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How to dynamically get the length of a div using JQuery and JavaScript?

I am developing a web application using AngularJS. I find myself in a situation where I have a bar (with the css I created a line) that must dynamically lengthen and shorten.
I know that JQuery scripts are sufficient to do this. For example, if my css is like this:
.my_line{
display:block;
width:2px;
background: #FFAD0D;
height: 200px; /*This is the part that needs to dynamically change*/
}
I could in the controller resize the line (of my_line class) simply with:
$(".my_line").css("height", someExpression*100 + 'px');
The thing is, I would like to dynamically resize the line based on the size of another div element (Or, in general, any HTML element of my choice).
I don't know how to get (at run-time) the size of a certain page element in terms of height.
Only in this way I would be able to create a line that dynamically lengthens or shortens as the size of a div (or some other element) changes!
How do you do this? So I will avoid writing hard-coded the measures but I want make sure that they vary as the dimensions of other elements on the page vary

I hope this is helping:
$(".my_line").css("height", $("#referenceElement").height()*5 + 'px');
.my_line{
display:inline-block;
width:2px;
background: #FFAD0D;
}
#referenceElement {
display:inline-block;
background: yellow;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="my_line"></div>
<div id="referenceElement">Hi, I'm 5 time smaller than the orange line!</div>

Here I am using the setInterval to track the div's height (you can do width as well) and storing it in a previousHeight variable and comparing it every interval
Then according to the comparison, it will determine if the height of the div has changed. If it has then it will change the height of the other div according to the height of the first div
You can create multiple variables and track multiple elements in the same setInterval
$(document).ready(function(){
var previousHeight = parseInt($("#my-div").css("height"));
setInterval(function(){ checkHeight(); }, 100);
function checkHeight() {
// Check height of elements here
var currentHeight = parseInt($("#my-div").css("height"));
if(currentHeight != previousHeight) {
previousHeight = currentHeight;
$("#dynamic-div").css("height", parseInt(currentHeight) + "px");
}
}
$("#button").click(function() {
$("#my-div").css("height", parseInt(previousHeight) + 5 + "px");
})
})
#my-div{
background: #000000;
height: 20px;
width: 20px;
}
#dynamic-div{
background: teal;
height: 20px;
width: 20px;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="my-div">
</div>
<button id="button">Increase div height</button>
<div id="dynamic-div">
</div>

How can I figure out what size an HTML Element will be? (tween size as element added)

I'm pretty sure this is currently infeasable.
I have an animation that involves an element moving from an absolute position to an inline one. For reasons, I can not know how the container is sized, nor how the element I'm animating is sized.
What I need to know is what the size of the HTML Element will be after the transformation, without any jittery drawing.
This makes the problem very difficult (likely undoable) because I have no way to know if adding the element will resize the parent, or resize the element itself.
What I need is a means of looking into the future.
const byId = (id) => document.getElementById(id);
#container {
height: 3em;
min-width: 50%;
background: teal;
}
#mystery {
background: purple;
}
<div id="container">
<div id="mystery">Some Text</div>
</div>
<button onClick='byId("mystery").style.position = "relative"'>Position Relative</button>
<button onClick='byId("mystery").style.position = "absolute"'>Position Absolute</button>
Currently, these are the only solutions I can imagine (they're all absurd):
Clone the entire webpage HTML, make the clone have opacity: 0; pointer-events: none and render what the future will be secretly.
Capture the paint data of the current page (basically screenshot), overlay that while secretly modifying the page, get my future, revert, and remove the screenshot overlay.
Similar to number 2, is there a way to ❄️freeze❄️ rendering of a page for 3-4 frames?
I remember seeing a "sizing worker" something-or-rather a long time ago. Couldn't find any information on it now, but it seems like it might be useful?

You can simply change the property, measure the sizes you want and then change the property back. JS is fast enough to do it all between renderings, as long as you keep it all in the same thread. Have you tried that at all?
Asker Edit:
Here's the code to prove it works.
function byId(id){ return document.getElementById(id); }
const tweenyEl = byId("tweeny");
function appendTweeny() {
tweenyEl.style.opacity = "1";
const startingWidth = tweenyEl.clientWidth + "px"
tweenyEl.style.position = "relative";
const targetWidth = tweenyEl.clientWidth + "px";
console.log(startingWidth, targetWidth);
tweenyEl.style.width = startingWidth;
requestAnimationFrame(() =>
requestAnimationFrame(() =>
tweenyEl.style.width = targetWidth
)
);
}
function resetTweeny() {
tweenyEl.style.position = "";
tweenyEl.style.width = "";
tweenyEl.style.opacity = "0.1";
}
#container {
display: inline-block;
height: 3em;
min-width: 150px;
background: teal;
}
#tweeny {
font-family: arial;
color: white;
position: absolute;
background: purple;
transition: all 0.5s ease;
opacity: 0.1;
}
<div id="container">
<div id="tweeny">I'm Tweeny</div>
</div>
<br>
<button onClick='appendTweeny()'>Append Tweeny</button>
<button onClick='resetTweeny()'>Reset Tweeny</button>

I would suggest cloning the page into an iframe and then positioning the iframe off the screen.
<iframe style="width:100vw;height:100vh;left:-101vw;positionabsolute"><iframe>

Also bear in mind that the user can zoom in-and-out at will! Different browsers might render the same thing in different ways. You really don't know how big an element will be until it does so.
I don't know if you can get anywhere by specifying display: none; ... whether or not the browser would bother to make these calculations for an object that isn't visible.

You can clone on the fly an element with same transformation with delay 0 and then calculate it's width and height, then do what you want with your actual element it's still animating

Iterate over Array on mouse move left or right over a div

I have an static Array of Strings and a div that contains a p element that contains one string at a time. What im trying to do is when you move across the div, you iterate over the array and change your text based on the current mouse position and thus position in the array.
The way i thought of doing this was
Getting div size in pixels, dividing this by the amounts of elements in the array.
Then i would check the mouseposition every time it changes and depending on its position (eg in the 52 section of the div) would change it to the 52 item in the array.
Am i overthinking this? Is there an easier way to do this?

Something like the solution below should work for you. Add a div/span/container of your choice for each string you want to add. Add an event listener that shows your string's container when you mouse-in, and removes the event listener when you mouse out. We use 'visibility: hidden' instead of 'display: none' to make sure your containing blocks still exist in the DOM.
Index.html:
<div class="container">
</div>
Main.css:
.container {
display: flex;
flex-direction: row;
background: #DDD;
width: 100%;
height: 200px;
}
.child {
width: 100%;
height: 100%;
color: black;
}
.hide {
visibility: hidden;
}
Index.js:
//Replace this with however you're getting your strings now
var stringContent = ["String #1", "String #2", "String #3"]
$(document).ready(function(){
//You can remove this if the number of strings are not dynamic and replace with the hardcoded html tags
for (var i = 0; i < stringContent.length; i++)
{
var eleToAdd = `<div class='child hide'>${stringContent[i]}</div>`
$(".container").append(eleToAdd)
}
$(".child").on("mouseenter", function(){
$(this).removeClass("hide");
})
$(".child").on("mouseout", function(){
$(this).addClass("hide");
})
})

Dynamic mouseenter

I appended a few divs with inside img tags. Every tag has own unique id = "theImg"+i where "i" is number. I want to mouseover on specific img and show the content of span (which also have specific id with number). Here is my code so far but not working.
var j;
document.onmouseover = function(r) {
console.log(r.target.id);
j = r.target.id;
}
$(document).on({
mouseover: function(e){
$("span").show();
},
mouseleave: function(e){
$("span").hide();
}
}, "img#"+j);

If you have a span after every img, maybe it's a good idea to not use JavaScript at all? ;-)
You could use :hover pseudoclass in CSS, making your thing always work reliably.
Consider the following example:
img + span {
display: none;
}
img:hover + span {
display: block;
}
/*/ Optional styles /*/
div {
position: relative;
float: left;
}
div img + span {
position: absolute;
color: #fff;
background: #27ae60;
border: solid 1px #2ecc71;
border-radius: 50px;
z-index: 1;
bottom: 1em;
width: 80%;
left: 50%;
margin-left: -43%;
padding: 2% 3%;
text-align: center;
}
<div>
<img src="https://placehold.it/400x200">
<span>This is an image of a gray rectangle!</span>
</div>
<div>
<img src="https://placehold.it/200x200">
<span>This is an image of a gray square!</span>
</div>
<div>
<img src="https://placekitten.com/g/400/200">
<span>This is an image of a cute kitten inside a rectangle!</span>
</div>
<div>
<img src="https://placekitten.com/g/200/200">
<span>This is an image of even cuter kitten inside a square!</span>
</div>

So the issue is that you are trying to set your handler on a dynamic selector ("img#"+j) but this will not work. For one thing, that equation will be evaluated only once, on page load, when j is undefined.
So you want to do this instead:
target only img tags for your mouse over... Better yet, give your special images all the same css class so you can attach the event handlers only to those. That will be more efficient.
When an image is moused over or out of, grab it's id attribute, extract the number from it, then use that to build a selector for the appropriate span to show.
var get_span_from_image = function(image) {
var image_id = image.attr("id");
var matches = image_id.match(/theImg(\d+)/);
if(matches) return $("theSpan" + matches[1]);
return $(); // nothing found, return an empty jQuery selection
};
$("img").hover(
function() { // mouse over
get_span_from_image($(this)).show();
},
function() { // mouse out
get_span_from_image($(this)).hide();
}
);
Note: There are better ways to "link" two nodes together, but this is just to answer your question with the current structure you have.
UPDATE: Some ideas to link two nodes together
So instead of trying to extract a number from an id attribute, a better way would be to tell either one of the image or span about it's sibling. You could output your html like this, for instance:
<img id="theImg1" data-target="theSpan1" class="hoverable" src="..."/>
....
<span id="theSpan1">...</span>
Of course now your ideas could be anything - you don't have to use numbered values or anything.
Then your hover code becomes quite simply:
var get_span_from_image = function(image) {
var span_id = image.data("target");
return $("#" + span_id);
};
$("img").hover(
function() { // mouse over
get_span_from_image($(this)).show();
},
function() { // mouse out
get_span_from_image($(this)).hide();
}
);
Hope this helps!

Automatically resize text area based on content [duplicate]

This question already has answers here:
Creating a textarea with auto-resize
(50 answers)
Closed 8 years ago.
On one of my pages, I have a text area html tag for users to write a letter in. I want the content below the text area to shift down, or in other words, I want the text area to resize vertically with each line added to the text area and to have the content below simply be positioned in relation to the bottom of the text area.
What I am hoping is that javascript/jquery has a way to detect when the words wrap, or when a new line is added and based on that do a resize of the text area container.
My goal is to make the content below the text area stay the same distance from the bottom of the text no matter how much a user writes.
The text area creates a scroll bar when the text overflows.

Since I wasn't too happy with several solutions I found on the web, here's my take on it.
Respects min-height, max-height.
Avoids jumping around and flashing the scrollbar by adding a buffer to the height (currently 20, may replace by line-height). However still shows scrollbar when max-height is reached.
Avoids resetting the container scroll position by incrementally reducing the textarea height instead of setting it to 0. Will thusly also remove all deleted rows at once. Works in IE and Chrome without browser sniffing.
http://jsfiddle.net/Nd6B3/4/
<textarea id="ta"></textarea>
#ta {
width:250px;
min-height:116px;
max-height:300px;
resize:none;
}
$("#ta").keyup(function (e) {
autoheight(this);
});
function autoheight(a) {
if (!$(a).prop('scrollTop')) {
do {
var b = $(a).prop('scrollHeight');
var h = $(a).height();
$(a).height(h - 5);
}
while (b && (b != $(a).prop('scrollHeight')));
};
$(a).height($(a).prop('scrollHeight') + 20);
}
autoheight($("#ta"));

http://www.jacklmoore.com/autosize/
Download the plugin first:
Step 1: Put "jquery.autoresize.min.js" where you keep your jquery plugins.
Step 2: Link the file in HTML -> <script src="jquery.autosize.min.js" type="text/javascript" ></script> Be sure that this link comes after your jquery link, and before your own javascript/jquery code links.
Step 3: In your javascript code file simply add $('#containerToBeResized').autosize();

$('textarea').keyup(function (e) {
var rows = $(this).val().split("\n");
$(this).prop('rows', rows.length);
});
this work sample.

See this Fiddle from this answer. That increases the height of the textarea based on the number of lines.
I think that's what you're asking for.
Copied the code from the answer below:
HTML
<p>Code explanation: Textarea Auto Resize</p>
<textarea id="comments" placeholder="Type many lines of texts in here and you will see magic stuff" class="common"></textarea>
JS
/*global document:false, $:false */
var txt = $('#comments'),
hiddenDiv = $(document.createElement('div')),
content = null;
txt.addClass('txtstuff');
hiddenDiv.addClass('hiddendiv common');
$('body').append(hiddenDiv);
txt.on('keyup', function () {
content = $(this).val();
content = content.replace(/\n/g, '<br>');
hiddenDiv.html(content + '<br class="lbr">');
$(this).css('height', hiddenDiv.height());
});
CSS
body {
margin: 20px;
}
p {
margin-bottom: 14px;
}
textarea {
color: #444;
padding: 5px;
}
.txtstuff {
resize: none; /* remove this if you want the user to be able to resize it in modern browsers */
overflow: hidden;
}
.hiddendiv {
display: none;
white-space: pre-wrap;
word-wrap: break-word;
overflow-wrap: break-word; /* future version of deprecated 'word-wrap' */
}
/* the styles for 'commmon' are applied to both the textarea and the hidden clone */
/* these must be the same for both */
.common {
width: 500px;
min-height: 50px;
font-family: Arial, sans-serif;
font-size: 13px;
overflow: hidden;
}
.lbr {
line-height: 3px;
}