How to get x-coordinate of a touch event point relative to the target element?

Question

So I have an image that looks like this:

var elem = document.getElementById("bt");
elem.addEventListener("touchstart", handleStart, false);

function handleStart(e) {
  e.preventDefault();
  var touch = e.targetTouches[0];
  X = touch.pageX;
  Y = touch.pageY;
  return [X, Y];
}

<img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/142996/sections-3.jpg" id="bt" width="900" height="600">

What I want to do, is get the x- and y-coordinates of a touch event relative to the image itself.

Answer 1

You can achieve that easily using Jquery.In my code I am showing using click event since i am using desktop but you can replace click by touch event.

FIDDLE

Here is the code:

$('.clickable').bind('click', function(ev) {
  var $div = $(ev.target);
  var $display = $div.find('.display');

  var offset = $div.offset();
  var x = ev.clientX - offset.left;
  var y = ev.clientY - offset.top;

  $display.text('x: ' + x + ', y: ' + y);
});

.clickable {
  border: 1px solid #333;
  background: #eee;
  height: 200px;
  width: 200px;
  margin: 15px;
  position: absolute;
}

.display {
  display: block;
  height: 16px;
  position: absolute;
  text-align: center;
  vertical-align: middle;
  width: 100%;
  top: 50%;
  margin-top: -8px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class='clickable'>
  <span class='display'></span>
</div>