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How to make cursor tooltip not go offscreen

I'm working on a popup box that shows some text some position away from an element when the cursor hovers over it. You can see a simplified demo here: https://jsfiddle.net/xsvm2Lur/61/
Right now the popup box will squash up when it is near the bounding box. I want the popup to appear to the bottom-left (if the popup will overflow to the right) or top-left (if the popup will overflow to the bottom and to the right) of the hovered element's position if the popup will overflow.
The position and text that will be shown are dynamically generated (e.g. I don't know before rendering).
Right now I have a working version using Javascript. The way I go about it is:
Get the text that will be displayed. Count the number of characters that is going to be displayed x 0.25em for each character to get the width of the text.
Calculate the width of the displayed string + padding (left and right). Let's call it textLength. This will be set as the popup's width so all the text goes into 1 line.
If textLength + x position of the cursor > box width, "invert" the popup box on the x-axis by deducting the popup's "left" value by textLength and some distance away from the element.
Repeat the same check for the y position, i.e. if cursor position + line height (1em) + bottom padding > box height, invert y.
The solution works, but I'm wondering if there's a better way to do this without character counting, or if there is another way to do it elegantly, maybe CSS only without Javascript?

Sadly, I don't believe there is a way to do it with CSS only. However, by working on your fiddle, I've managed to add the functionality you wanted.
The way I went about it was just to include a reference to the container and check whether the popup position and size were inside the container BoundingClientRect.
This is the updated code for the popupShow function:
const showPopup = (top, left, text, container) => {
popup.textContent = text;
const containerBCR = container.getBoundingClientRect();
const popupBCR = popup.getBoundingClientRect();
const popupWidth = popupBCR.width,
popupHeight = popupBCR.height;
let popupTop = top + 20,
popupLeft = left + 20,
newPopupWidth;
console.log("height: ", popupHeight);
console.log("top: ", top);
console.log("bottomPopup: ", top + 20 + popupHeight);
console.log("bottomBoundary", containerBCR.bottom);
if (left + 20 + popupWidth > containerBCR.right) {
popupLeft = left - popupWidth;
if (popupLeft < containerBCR.left) {
popupLeft = containerBCR.left;
newPopupWidth = left - containerBCR.left;
}
}
if (top + 20 + popupHeight > containerBCR.bottom) {
popupTop = top - popupHeight;
if (popupTop < containerBCR.top) {
popupTop = containerBCR.top;
}
}
popup.style.top = popupTop + "px";
popup.style.left = popupLeft + "px";
popup.style.width = newPopupWidth;
popup.style.visibility = 'visible';
}
As you can see, I've also edited the popup to use "visibility: hidden" instead of "display: none". This is because if the display is set to "none", we won't be able to get his size (there might be workarounds for this, though).
Try checking out the updated fiddle and tell me what you think.
I've pushed one circle a little bit further down because the code doesn't currently check for the padding of the popup, so it was overflowing a little (few pixels).

This is based on quadrants, simple calculates if we are over 50% width and/or height and swaps the style to use the right or bottom instead. This doesn't care about the content of the popup, no measuring required.
const popup = document.getElementById("pop-up")
const parsePx = (px) => parseFloat(px.slice(0, -2))
const showPopup = (text, position) => {
popup.textContent = text;
popup.style.top = position.top;
popup.style.left = position.left;
popup.style.right = position.right;
popup.style.bottom = position.bottom;
popup.style.display = 'inline-block';
}
const hidePopup = () => {
popup.style.display = 'none';
}
const circles = document.querySelectorAll(".red-circle")
circles.forEach(el => el.addEventListener('mouseover', (e) => {
const hoveredEl = e.target;
const textContent = hoveredEl.getAttribute('data-content');
//get absolute position of elements
let elBounds = hoveredEl.getBoundingClientRect();
//get absolute position of parent;
let ctBounds = popup.parentElement.getBoundingClientRect();
//calculate relative positions
let left = elBounds.left - ctBounds.left + (elBounds.width / 2),
top = elBounds.top - ctBounds.top + (elBounds.height / 2),
width = ctBounds.width,
height = ctBounds.height
//prepare position settings
let position = { left: "auto", top: "auto", bottom: "auto", right: "auto" }
//calculate if we're over 50% of box size
if(top>ctBounds.height/2) position.bottom = ctBounds.height - top + 20 + 'px'; else position.top = top + 20 + 'px';
if(left>ctBounds.width/2) position.right = ctBounds.width - left + 20 + 'px'; else position.left = left + 20 + 'px';
showPopup(textContent, position);
}))
circles.forEach(el => el.addEventListener('mouseout', (e) => { hidePopup() }))
.container { width: 200px; height: 200px; border: 1px solid black; position: relative;}
.red-circle { border-radius: 50%; background: red; width: 20px; height: 20px; position: absolute;}
#pop-up { background-color: #EFEFEF; padding: 0.25em; position: absolute;}
<div class="container">
<div style="top:20px;left:20px;" class="red-circle" data-content="This is a red circle"></div>
<div style="top:10px;left:150px;" class="red-circle" data-content="This is the top-right red circle"></div>
<div style="top:140px;left:150px;" class="red-circle" data-content="This is the bottom-right red circle"></div>
<div style="top:140px;left:15px;" class="red-circle" data-content="This is the bottom-left red circle"></div>
<span style="display:hidden" id="pop-up"></span>
</div>

jquery get width of div to left side window

And I want to get the width or distance or pixel that between the div and left side of of window/viewport.
And another width again between the div to the right side of the window.
I will use the width to create a left line and right line.
But I am poor in jQuery, I try offset but seems nothing happen.
So I back to 0 again so I didn't include fiddle here since I got nothing inside.
But I have attached with the image link as below, to explain my question.
Please help me on try to get the width, I can create the line myself.
Thank you.

var of = $(ele).offset(), // this will return the left and top
left = of.left, // this will return left
right = $(window).width() - left - $(ele).width() // you can get right by calculate
Maybe this can help you.
After all, .width() isn't the only answer, like innerWidth() or outerWidth()

There is two options
One is you can use red line as image and you can place the div over the red line.
Second one,
If you want to calculate:
Left div width = parent div width - child div offset;
Right div width = parent div width - child div offset + child div width;
var parentdiv = document.getElementById("ParentDivID");
var parentWidth = parentdiv.offsetWidth;
var childdiv = document.getElementById("childDivID");
var childWidth = childdiv.offsetLeft;

This is easier to do with POJ (plain old javascript). Get the position of the element on the screen. Then evaluate its left property. That will be the width of your left line. Then subtract its right property from the width of the screen. That will be the width of your right line.
var x = document.getElementById('myDiv').getBoundingClientRect();
var myLeftLineWidth = x.left;
var myRightLineWidth = screen.width - x.right;
For more information see this post.
If you want the width of the window instead of the screen, change screen.width to window.innerWidth. If you don't want the scrollbar, etc. to be included in the width, use document.documentElement.clientWidth. (For more info on these, see this.)

We can work out that where the box starts with .offset().
Next, we can work out where the box ends with .offset() + .width().
We now know where our box sits on the x-axis.
Now let's see what we have to the left of our box with .left which can run on our .offset().
We've now worked out how much space there is to the left and how wide our box is.
Finally, we can put what we've worked out together, we can get the page width $(window).width() and minus what there is to the left of our box (stage 2) and the width of our box (stage 1) and that will only leave what is to the right of our box.
That's the theory anyway now let's have a look at some code. You'll see I'm working out all the bits from the theory and then adding some visual representation.
calcSizes = function() {
var boxPos = $(".box").offset(),
toLeft = boxPos.left,
toRight = $(window).width() - ($(".box").width() + toLeft);
$(".left").width(toLeft + "px");
$(".right").width(toRight + "px");
console.log("Right: " + toRight + "px");
console.log("Left: " + toLeft + "px");
console.log("Width: " + $(".box").width() + "px");
console.log(
$(window).width() + "px = " +
toRight + "px + " +
toLeft + "px + " +
$(".box").width() + "px"
);
console.log(" ");
}
calcSizes();
body {
margin: 0
}
.box,
.indicator {
padding: 10px 0;
text-align: center
}
.box {
width: 100px;
background: #FF5722;
margin-left: 60%
}
.indicator {
background: repeating-linear-gradient( 45deg, #F44336, #F44336 10px, #D32F2F 10px, #D32F2F 20px);
overflow: hidden;
transform: translatey(-100%);
opacity: .8
}
.left {
float: left
}
.right {
float: right
}
button {
position: fixed;
top: 55px;
left: 30px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="box">BOX</div>
<div class="left indicator">
LEFT
</div>
<div class="right indicator">
RIGHT
</div>
<button onclick="calcSizes()">
Recalculate
</button>
Hope this makes sense and helps you with your project.

You can do that with JavaScript, no need for jQuery:
var mydiv = document.getElementById('mydiv');
var offset = mydiv.getBoundingClientRect();
var offsetRight = document.documentElement.clientWidth - offset.right;
var offsetLeft = offset.left;
JSFiddle

Touch drag-and-drop positioning near tap with JS

I want to make function to drag and drop some elements on my page. When I use code below, the element moves by touch, but it is not staying near finger where I tapped (for expample in the center or left/right bottom of the element), but it moves to right bottom from the finger. What I want - is to be able to move element dragging it by point where I tapped.
function touchStart(e) {
e.preventDefault();
var whichArt = e.target;
resetZ();
whichArt.style.zIndex = 10;
}
function touchMove(e) {
e.preventDefault();
var dragElem = e.target;
var touch = e.touches[0];
var positionX = touch.pageX;
var positionY = touch.pageY;
dragElem.style.left = positionX + 'px';
dragElem.style.top = positionY + 'px';
}
document.querySelector('body').addEventListener('touchstart', touchStart, false);
document.querySelector('body').addEventListener('touchmove', touchMove, false);
<!--elements I want to drag-->
<img draggable="true" id="one" src="images/one.svg" style="position: absolute; left: 50px; top: 120px; z-index: 3;">
<img draggable="true" id="two" src="images/two.svg" style="position: absolute; left: 367px; top: 150px; z-index: 3;">
I also tried to different things to calculate left and right position, but it failed, for example:
var moveOffsetX = dragElem.offsetLeft - touch.pageX;
var moveOffsetY = dragElem.offsetTop - touch.pageY;
var positionX = touch.pageX - moveOffsetX; /* + also tried*/
var positionY = touch.pageY - moveOffsetY; /* + also tried*/
So how is it possible to accomplish the right behaviour?

It happens because the anchor point of the element is on the top left corner.
Try this in your touchMove function:
dragElem.style.left = positionX - dragElem.width / 2 + 'px';
dragElem.style.top = positionY - dragElem.height / 2 + 'px';
Here is a working fiddle. You can test it on chrome using the device mode in the developer tools.
PS. you should have a touchend event to re-initialize the z-index (if you did not already do that).
Edit
So, in the touchstart event , you must save the anchor of the element (where the user touched the element).
To do so, you can use getBoundingClientRect() function. It's better than to depend on the style, top/left attributes because they may not be specified :
var elementRect = whichArt.getBoundingClientRect();
anchor = {
top: touch.pageY - elementRect.top,
left: touch.pageX - elementRect.left
};
And then you use this anchor to compute top/left instead of the center of the element (as I thought at first).
Here is the updated fiddle

Calculating child div top position - why does parent offsetHeight need to be subtracted?

I have created a magnifier in pure js. What I discovered in needing to translate the mouse position of a div relative to its parents is that in calculating the top for the overlaying magnifier div, the offsetTop works differently than the offsetLeft. After adjusting for what should be the top, I need to subtract the whole container div's offsetHeight.
The line in the code in question is this:
magnifier.style.top = yPosition - container.offsetHeight + "px";
Why do I need to subtract container.offsetHeight?
I know I've read something regarding this, but can't find it.
Disclaimers This code is working. I am asking so I (and those following) can understand how the box model works.
I know there are jQuery alternatives that are more cross browser reliable. I like to code it myself so that I can learn how it all works. If you see something which is not compatible for a modern browser, feel free to comment.
Lastly, For anyone using this, I removed code from this example to adjust for transforms. For example, if the wrapper has a transform: translate(-50%, 0); to center the wrapper horizontally, you will need to add the resulting amount of the translation (which translates to the wrapper's left position) back into the calculation.
I have created a jsfiddle here. I left more comments in the Fiddle as to methodology if anyone is interested.
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="../css/ms.js"></script>
<style type="text/css">
/********************/
body {
background-color: #FFF;
margin-left: 30px;
margin-top: 10px;
}
.wrapper {
position: absolute;
left: 100px;
}
#container {
width: 527px;
height: 450px;
border: 5px black solid;
overflow: hidden;
background-color: #F2F2F2;
cursor: pointer;
}
#image {
width: 527px;
height: 450px;
}
#magnifier {
width: 250px;
height: 250px;
overflow:hidden;
position:relative;
z-index: 1000;
border: solid 1px;
}
#magnifier img {
position: absolute;
}
</style>
</head>
<body>
<div class="wrapper" id="wrapper">
<div id="container">
<img id="image" src="../docs/grade-2/jpg/g2-bb-saints-francis.jpg">
<div id="magnifier" class="magnifier">
<img id="imagecopy">
</div>
<br>
</div>
<input type="button" value="Zoom" onClick="initmagnifier('magnifier', 'image', 'imagecopy');"><br>
</div>
<script>
function initmagnifier(magnifier, image, imagecopy){
var magnifier = document.getElementById("magnifier");
var container = document.getElementById("container");
var wrapper = document.getElementById("wrapper");
var img = document.getElementById(image);
var imgcopy = document.getElementById(imagecopy);
var zoom = 2;
container.addEventListener("mousemove",
function(e){
movemagnifier(e, img, imgcopy, magnifier, container, wrapper, zoom)
}, false);
var src = img.src;
imgcopy.src = src;
var src2 = imgcopy.src;
imgcopy.height = img.height * zoom;
imgcopy.width = img.width * zoom ;
}
function movemagnifier(e, img, imgcopy, magnifier, container, wrapper, zoom) {
// to get the left & top of the magnifier
// position needs to be adjusted for WRAPPER & CONTAINER top and left
// gets the top and left of the container
var containerPosition = getPosition(e.currentTarget);
// adjust out the CONTAINER's top / left
// Then takes 1/2 the hight of the MAGNIFIER and subtracts it from the MOUSE position to center MAGNIFIER around the MOUSE cursor
var xPosition = e.clientX - containerPosition.x - (magnifier.clientWidth / 2);
var yPosition = e.clientY - containerPosition.y - (magnifier.clientHeight / 2);
magnifier.style.left = xPosition + "px";
magnifier.style.top = yPosition - container.offsetHeight + "px";
// Adjust for zoom
// adjust the MAGNIFIER's top/left at an equal pace to the zoom amount
var yTravel = (e.clientY - containerPosition.y ) * (zoom - 1);
var yimgPosition = -(yPosition - container.clientTop + yTravel);
imgcopy.style.top = yimgPosition + "px";
var xTravel = (e.clientX - containerPosition.x) * (zoom - 1); // * 1.5
var ximgPosition = -(xPosition + xTravel);
imgcopy.style.left = ximgPosition + "px";
console.log('****');
console.log(e.clientY); // MOUSE POSTION
console.log(containerPosition.y);
console.log(wrapper.offsetTop);
console.log(wrapper.clientHeight);
console.log(container.offsetTop);
console.log(container.clientHeight);
console.log(yPosition);
console.log(container.offsetHeight);
console.log(magnifier.style.top);
}
function getPosition(element) {
var xPosition = 0;
var yPosition = 0;
// element is the CONTAINER
// This calculates the postion of the element (CONTAINER) TOP & LEFT relative to ALL parents
while (element) {
// if transform: translate in place for x and y,
// add it back as it skews the offsetLeft offsetTop values by the translate amount
xPosition += ((element.offsetLeft) - element.scrollLeft);
yPosition += ((element.offsetTop) - element.scrollTop);
element = element.offsetParent;
}
return { x: xPosition, y: yPosition };
}
</script>
</body>
</html>

It took me longer than I care to admit, but I have found the reason. In your fiddle you position the #magnifier-element relative, which means you have to move it from its 'natural' position, which is below the image inside the container.
So with every move you have to compensate for this, by pulling the #magnifier to the top/left position of the container, the left position already matches, but the 'natural' top position of the #magnifier is the full height of the container, as you calculate from the top/left position of the #container, you need to subtract the #container height.
A simple fix is to add position: relative to the #container and change position: relative on the #magnifier to position: absolute.
This will give you the expected coordinate system for the #magnifier as top: 0; left: 0 for the absolute positioned element is the top left corner of the its relative parent (the first positioned parent element, in this case #container).
a working example without the need to to subtract container.offsetHeight.
While I'm at it, you may want to look into the Element.getBoundingClientRect function, as you can get all information you need to determine the position in a single call.

calculate centered absolute div inside relative

I'm using 2 Javscript methods to position a hovering button inside a static element on my page. The button that is centered is inputted inside the first element and uses position absolute. The code I'm using to get the parent element measurements:
// calculate if the element is in the visible window
function elementVisibleRect(element) {
element = $(element);
var rect = {
top: Math.round(element.offset().top),
left: Math.round(element.offset().left),
width: Math.round(element.outerWidth()),
height: Math.round(element.outerHeight())
};
var scrollTop = $(window).scrollTop();
var windowHeight = $(window).height();
var scrollBottom = scrollTop + windowHeight;
var elementBottom = Math.round(rect.height + rect.top);
if (scrollTop < rect.top && scrollBottom > elementBottom) {
return rect;
}
if (scrollTop > rect.top) {
rect.top = scrollTop;
}
if (scrollBottom < elementBottom) {
rect.height = scrollBottom - rect.top;
} else {
rect.height = windowHeight - (scrollBottom - elementBottom);
}
return rect;
}
and for using this information and centering the button inside
// center the element based on visible screen-frame
function elementPosition (element) {
var visibleRect = elementVisibleRect(element);
$('.editHoverButton').css({
top: visibleRect.top + ((visibleRect.height / 2) - ($('.editHoverButton').outerHeight() / 2)),
left: visibleRect.left + (visibleRect.width / 2) - ($('.editHoverButton').outerWidth() / 2)
});
}
Now my problem is that a third party library requires the parent DIV to change position from the browser default "static" to "relative" which breaks my calculations in the second function.
It might be late, but no matter what I try I can't seem to figure out how to get this working for when the parent element has position set to relative. I can't seem to get the maths quite right, and my head is beginning to hurt. Any suggestions?
EDIT - ADDED JSFIDDLE
http://jsfiddle.net/RhTY6/

Elements with absolute positioning are removed from the natural flow (e.g. they don't leave a space where they were) and positioned relative to their first parent with non-static positioning. Since the positioning of the right-hand box is relative (not static), you can position the button with top: 50%; and left: 50%;. This will make the top-left corner at the center of the parent. Then all you have to do is subtract half the element's height and width from the position, using margin-top and margin-left. This is much simpler than what you were doing, as you can see below:
JavaScript:
function elementPosition() {
$('.editHoverButton').css('margin-top', 0 - $('.editHoverButton').outerHeight() / 2);
$('.editHoverButton').css('margin-left', 0 - $('.editHoverButton').outerWidth() / 2);
};
CSS:
.editHoverButton {
position: absolute;
z-index: 99;
font-family: sans-serif;
font-size: 14px;
font-weight: normal;
background-color: #00bb00;
top: 50%;
left: 50%;
}
Nothing else has to change except to remove this from the elementPosition() function.
DEMO (Notice that the left one no longer works. This is because it is positioned static.)
EDIT--Using the same basic idea, this method should work:
The problem is that you have take the top and left positions of the element when defining rect. on the positioning calculations. Changing those to 0 (not the best method, but it works) fixes the problem for relative elements.
DEMO (Notice that the left one now does work. This is because it is positioned at 0,0 anyway.)
EDIT--This will work when the page scrolls:
This sets the container in a variable so that when the page scrolls, it can be repositioned automatically.
DEMO

EDIT: made it worked with your CSS and HTML (relative and absolute positioning) by altering the Script only.
The horizontal axis calcs were completely missing (I've applied the same calcs you applied to the vertical axis).
I've added some data and a ruler to help you finish the job: as you can see, it is (and it was, in your original fiddle) not perfectly centered (obviously you need to look at it when the container is smaller than the viewport), but this will be easy to work out.
Running Demo
Try to resize the fiddle window and to scroll both vertically and horizontally to see it works.
function elementVisibleRect(element) {
$("#data").html("");
element = $(element);
var rect = {
top: Math.round(element.offset().top),
left: Math.round(element.offset().left),
width: Math.round(element.outerWidth()),
height: Math.round(element.outerHeight())
};
var scrollTop = $(window).scrollTop();
var windowHeight = $(window).height();
var scrollBottom = scrollTop + windowHeight;
var elementBottom = Math.round(rect.height + rect.top);
var scrollLeft = $(window).scrollLeft();
var windowWidth = $(window).width();
var scrollRight = scrollLeft + windowWidth;
var elementRight = Math.round(rect.width + rect.left);
addData("rect.top", rect.top);
addData("rect.left", rect.left);
addData("rect.width", rect.width);
addData("rect.height", rect.height);
addData("scrollTop", scrollTop);
addData("windowHeight", windowHeight);
addData("scrollBottom", scrollBottom);
addData("elementBottom", elementBottom);
addData("scrollLeft", scrollLeft);
addData("windowWidth", windowWidth);
addData("scrollRight", scrollRight);
addData("elementRight", elementRight);
if (rect.top < scrollTop) {
rect.top = scrollTop;
}
if (scrollBottom < rect.top < scrollTop) {
rect.top = scrollTop;
}
if (scrollBottom < elementBottom) {
rect.height = scrollBottom - rect.top;
} else {
rect.height = windowHeight - (scrollBottom - elementBottom);
}
if (rect.left < scrollLeft) {
rect.left = scrollLeft;
}
if (scrollRight < rect.left < scrollLeft) {
rect.left = scrollLeft;
}
if (scrollRight < elementRight) {
rect.width = scrollRight - rect.left;
} else {
rect.width = windowWidth - (scrollRight - elementRight);
}
return rect;
}