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Is there a way to add "active" class to list item based on its location in a div?

I've got a fixed height div with a list of clickable list items. In the middle of the div, I have an absolute positioned line that is meant to signify a selected item. Right now, it's just a static line.
Is there a way to add an active class to the list item as it is "selected" by the line?
http://dev.chrislamdesign.com/shortwave/

One of the solutions is to use document.elementFromPoint(x, y) method. Something like this:
let lineCoords, lineTop, lineCenter;
// try to remove these two lines, leave just the scroll event listener
// document.getElementById('scrollUp1').addEventListener('click', setActive);
// document.getElementById('scrollDown1').addEventListener('click', setActive);
// 2nd edition: added these event listeners
window.addEventListener('scroll', getLineCoords);
window.addEventListener('load', getLineCoords);
// added this line
document.getElementById('wrap-scroll-1').addEventListener('scroll', setActive);
function setActive() {
const li = document.elementFromPoint(lineCenter, lineTop + lineCoords.height);
clearActive();
li.classList.add('active');
}
function clearActive() {
const ul = document.getElementById('ul-scroll-1');
const activeLi = ul.querySelector('li.active');
if (activeLi) {
activeLi.classList.remove('active');
}
}
// 2nd edition: added this function
function getLineCoords() {
lineCoords = document.querySelector('.orange-line').getBoundingClientRect();
lineTop = lineCoords.top;
lineCenter = lineCoords.left + (lineCoords.width / 2);
}
You can see this in action here: JsBin. These up and down buttons are assumed to scroll the list, but I don't have this functionality, because that's not a point here - just scroll it youself. The point here is that the element under the orange line will get active class each time you click one of these buttons.
So, take this code and edit it as you want.
Edited: I added an scroll event listener to the #wrap-scroll-1 container, because I guess the scroll event occurs right on it. If not - you can change it. Look at this in action: JsBin
2nd edition: Added event listeners to reassign the orange line coordinates every time when the page scrolled, and also when the page is loaded. Take a look at the result here: JsBin

You could compare the rects of the line and each option to find which is selected:
const line = document.querySelector('#emotional .orange-line');
const options = document.querySelector('#emotional .selection-options').children;
const lineY = line.getBoundingClientRect().y;
const optionAfterSelected = [...options].find((option) => {
return option.getBoundingClientRect().y > lineY;
});
const selected = optionAfterSelected.previousSibling;
selected.classList.add('selected');
The selected option is the one with the largest y value without exceeding the y value of the orange line. To make things simple, the loop just returns the first option with a y value greater than the line, then grabs its previous sibling.
Update
To get this code to run whenever the user scrolls, you can wrap it in a function and attach it as an eventListener:
function updateSelection(menuId) {
const line = document.querySelector(menuId + ' .orange-line');
const options = document.querySelector(menuId + ' .selection-options').children;
const lineY = line.getBoundingClientRect().y;
const optionAfterSelected = [...options].find((option) => {
return option.getBoundingClientRect().y > lineY;
});
const selected = optionAfterSelected.previousSibling;
selected.classList.add('selected');
}
document.querySelector('#emotional .wrap-container').addEventListener('wheel', () => {
updateSelection('#emotional');
});
document.querySelector('#genre .wrap-container').addEventListener('wheel', () => {
updateSelection('#genre');
});
document.querySelector('#cinematic .wrap-container').addEventListener('wheel', () => {
updateSelection('#cinematic');
});

Input not scrolling to the far right like it should

I have an input field where i append data at the cursor position.
after that, i set the selectionStart to the end of the field.
BUT, whenever i add something to the input (by button clicks), i only see the left part of it (until it reaches the right edge). everything more is there (i can select it with the mouse and scroll), but it doesn't automatically show the right edge.
how can i do that?
i want to add something to the input and jump right to the end of the string.
// add 2 digit number
$('button#2digit').on('click', function add2digit() {
addNumberToInput(10, 99);
});
function addNumberToInput(min, max) {
var problemInput = $('input#testProblem');
if (lastCharIsOperation() || problemInput.val().trim() < 1) { // if last char is an operation or first in string, just append the number
addAtCursor(randomNonPrime(min, max));
} else {
addAtCursor('+' + randomNonPrime(min, max));
}
}
function addAtCursor(toAdd) {
var problemInput = $('input#testProblem');
var oldText = problemInput.val();
var cursor = problemInput[0].selectionStart;
var pre = oldText.substring(0,cursor);
var post = oldText.substring(cursor, oldText.length);
//insert at cursor
problemInput.val(pre + toAdd + post);
//put cursor to end
problemInput[0].selectionStart = problemInput.val().length;
}
(it even skips back to the left on blur, i couldn't make a picture with the windows snipping tool, because i had to click it first)

From Set mouse focus and move cursor to end of input using jQuery.
var problemInput = $('input#testProblem');
problemInput.focus();
var t=problemInput.val();
problemInput.val('');
problemInput.val(t);
Here is the start of a full solution: https://jsfiddle.net/michaelgentry/vwm159pt/

This will still cause the scroll to jump back to the left on blur, but does what you are asking:
var elem = document.getElementById('myInput');
elem.focus();
elem.scrollLeft = elem.scrollWidth;

Create a child div accordingly if another child already exists at that location (x,y)

I am inserting a textarea to a side bar (exactly on the right to), wherever a click is made on the page. The code is:
$('#page_to_be_clicked').click(function(e){
var offset = $(this).offset();
var comment_box_y_coord = e.pageY - offset.top;
alert(comment_box_y_coord);
$("#sidebar").append('<textarea id="cmmnt" rows="4" cols="10" '+
'style="position:absolute;top:'+comment_box_y_coord +
'px;left:5px"></textarea>');
})
The problem with this is that, if a textarea is already present at the location, it will overlap the existing, i.e. if a click is made twice at the same point on the page, then two textareas are created on top of each other. Instead, it should be created one below the other.
Is there a way to check, if a child already exists at the required co-ordinates?
Any help will be appreciated. Thanks.
How exactly should the textareas appear on clicks in a sequence:

This needs to be tested properly, but I think you need to do this:
DEMO
In your function change this line:
var comment_box_y_coord = checkCoords(e.pageY - offset.top);
and then add this function:
function checkCoords(y) {
if ($("textarea").length>0) {
$ts = $("textarea");
for (var i = 0; i<$ts.length;i++) {
var $ti = $ts.eq(i),
tcoords = [$ti.offset().top, $ti.offset().top+$ti.height()]
if (y>=tcoords[0] && y <= tcoords[1]) {
y = tcoords[1]+3;
}
}
}
return y;
}

change class of div on scroll HTML5 with data attribute

What I am trying to do is to call a function every time a person scrolls that checks the current class of container and adds +1 to the current value of the current data attribute and then toggles the class relative to the data attribute it is currently changing the class on scroll but giving a "NaN. I am already running this function on click and it works fine.
here is a fiddle.
http://jsfiddle.net/kaL63/1/
This is my function on scroll
var timeout;
$(window).scroll(function() {
if(typeof timeout == "number") {
window.clearTimeout(timeout);
delete timeout;
}
timeout = window.setTimeout( check, 100);
});
My html Looks like this
<div class="container year-1987" data-year-index="1987">
Some Content
</div>
the function I am calling right now that I think should work..
function check(){
var
animationHolder = $('.container'),
currentClass = animationHolder.attr("class").match(/year[\w-]*\b/);
var goToYear = $('.container').data('year-index');
var goToYear2 = parseInt(goToYear,1000) + 1;
animationHolder.toggleClass(currentClass + ' year-' + goToYear2);
animationHolder.attr('data-year-index', goToYear2);
}
My working code on click
$("a").click(function (e) {
e.preventDefault();
var
animationHolder = $('.container'),
currentClass = animationHolder.attr("class").match(/year[\w-]*\b/);
var goToYear = $(this).data('year-index');
animationHolder.toggleClass(currentClass + ' year-' + goToYear);
animationHolder.attr('data-year-index', goToYear);

I rewrote your check method:
function check() {
var $container = $('.container'),
currentYear = $container.data('m-index'),
nextYear = 1 + currentYear;
$container.removeClass('m-' + currentYear).addClass('m-' + nextYear);
$container.data('m-index', nextYear);
}
I made the following changes:
There is no need for the regular expression since we can generate the class name ourselves.
I am not sure why you were originally using two separate data-attributes (m-index and year-index), but I switched them to both match. If you need both of them, some more logic is needed to use year-index after the initial call.
I am now updating m-index via .data() rather than setting a data attribute.
This method seemed to work fine for me.

JavaScript, using a function to change the text displayed in a HTML <p> tag

I have a HTML5 canvas, which is displaying a number of images and a paragraph of text on the page underneath the canvas. I want the text in the paragraph to be updated to display a different element from a JS array depending on which image the user clicks on.
Currently, I have a 'mousedown' function that looks like this:
_mousedown: function(evt) {
this._setUserPosition(evt);
var obj = this.getIntersection(this.getUserPosition());
if(obj && obj.shape) {
var shape = obj.shape;
this.clickStart = true;
shape._handleEvent('mousedown', evt);
isClickOnImage(evt);
var id = shape.id;
selectTip(id);
}
//init stage drag and drop
if(Kinetic.DD && this.attrs.draggable) {
this._initDrag();
}
}
I tried using the line var id = shape.id to update the ID that's being passed to the function, so that it will get the correct element from my 'tips' array, but for some reason, when I view the page in the browser, and click on an image, the text beneath the canvas is not updated. It seems that this function is not updating the 'id' variable to the ID of whichever image has been clicked.
After looking into this, it seems to me that I will want to use a loop inside the 'mousedown' function, that will take the 'id' of the image on which the click has been detected, and loop through my 'sources' array (which is where all of the images have been loaded from the HTML into the JS), checking at each position whether the image stored at that location has the same ID as that of the image that has been clicked on. If it does, the loop should set the text to the text stored at that position of the array, and if not, it should continue looking through the array until it find it. Would this make sense? I tried adding the following code to the 'mousedown' function, but it doesn't change the text as I expected:
var imageCheckArray = 0;
while(imageCheckArray < sources.length){
if(shape.id == sources[imageCheckArray]){
selectTip(imageCheckArray);
} else {
imageCheckArray++;
}
}
Is there something I'm missing from the loop?
The code for the whole function currently looks like this:
_mousedown: function(evt) {
this._setUserPosition(evt);
var obj = this.getIntersection(this.getUserPosition());
if(obj && obj.shape) {
var shape = obj.shape;
this.clickStart = true;
shape._handleEvent('mousedown', evt);
isClickOnImage(evt);
/*This line needs to get the element of the sources array that has been selected,
and then select the element at the same position from the tips array.*/
//var id = null;
var imageCheckArray = 0;
while(imageCheckArray < sources.length){
if(shape.id == sources[imageCheckArray]){
selectTip(imageCheckArray);
} else {
imageCheckArray++;
}
}
//var id =
//selectTip(id);
}
//init stage drag and drop
if(Kinetic.DD && this.attrs.draggable) {
this._initDrag();
}
}
Edit 11/01/2013 # 16:10
The code for selectTip is:
function selectTip(id){
$("#tipsParagraph").text(tips[id]);
}
and I've put a jsFiddle up here: http://jsfiddle.net/cd8G7/ although the 'result' panel is not showing what I actually see when I view the page in my browser- I get the canvas with all of the images displayed, and the paragraph underneath the canvas shows the text from the first element of my 'tips' array.
Edit 23/01/2013 # 13:50
Here's my isClickOnImage function:
function isClickOnImage(event){
var clickX = event.clientX;
var clickY = event.clientY;
//var imageCheckIteration = 0;
while(imageCheckIteration < sources.length){
if((clickX > sources[imageCheckIteration].x && clickX < sources[imageCheckIteration].x + imageWidth) &&
(clickY > sources[imageCheckIteration].y && clickY < sources[imageCheckIteration].y + imageHeight)){
/*This is where I need to print the variable that holds the text I want to display, but I need to display its contents
outside the canvas, in the <p></p> tags below. */
console.log("Click on image detected");
document.getElementById("tipsParagraph").innerHTML = sources[imageCheckIteration].data-tip /*tips[imageCheckIteration]*/;
} else {
document.getElementById("tipsParagraph").innerHTML = "";
}
}
}
What I intended that this function do is, capture the X & Y coordinates of any click on the canvas, and store them in the variables "clickX" and "clickY". Then, I have a variable called "imageCheckIteration" that has been initialised to 0, and while this variable is less than the length of my "sources" array (which is the array where all of the images have been stored), the function should check whether the click was on an area of the canvas that is covered by one of the images in the array.
If it was, then a console log should display the message "click on image detected", and the line
document.getElementById("tipsParagraph").innerHTML = sources[imageCheckIteration].data-tip;
should set the value of the "tipsParagraph" to be the value of the 'data-tip' attribute of whichever image is at the 'imageCheckIteration' position of the 'sources' array. If the click was detected on an area of the canvas that does not have an image displayed, then the value of the "tipsParagraph" should be set to hold nothing.
However, for some reason, when I view the page in the browser, the 'tipsParagraph' displays the text "This is where the text will be displayed", which is its default value, so that's fine. But, when I click on an image, or click anywhere else on the canvas, the text displayed in the 'tipsParagraph' is not updated.
I can't figure out why this is- can someone point me in the right direction? Does it mean that my isClickOnImage(event) function is never being called?

I simplified the way you are getting a reference to an image through the canvas. The trick here is to swap the z-index of the canvas and the image container and grab the reference to the image on the mouse up event. I don't know of a clean way to get elements behind a canvas, hence the workaround.
$('canvas').bind('mousedown', function(e) {
$('section').css('z-index', 4);
});
$('img').bind('mouseup', function(e) {
$('#tipsParagraph').text($(this).attr('id') + ":" + $(this).attr('alt'));
$('section').css('z-index', 2);
});
The second portion here is grabbing some attributes from the image itself and updating the text inside your div.
You can see more of the solution here.