js coordinates of bottom text selection

js-coordinates-of-bottom-text-selection.js

function getSelectionCoords(win) {
        win = win || window;
        var doc = win.document;
        var sel = doc.selection, range, rects, rect;
        var x = 0, y = 0;
        if (sel) {
          if (sel.type != "Control") {
            range = sel.createRange();
            range.collapse(true);
            x = range.boundingLeft;
            y = range.boundingTop;
          }
        } else if (win.getSelection) {
          sel = win.getSelection();
          if (sel.rangeCount) {
            range = sel.getRangeAt(0).cloneRange();
            if (range.getClientRects) {
              range.collapse(true);
              rects = range.getClientRects();
              if (rects.length > 0) {
                rect = rects[0];
              }
              x = rect.left;
              y = rect.bottom;
            }
            if (x == 0 && y == 0) {
              var span = doc.createElement("span");
              if (span.getClientRects) {
                span.appendChild(doc.createTextNode("\u200b"));
                range.insertNode(span);
                rect = span.getClientRects()[0];
                x = rect.left;
                y = rect.bottom;
                var spanParent = span.parentNode;
                spanParent.removeChild(span);
                spanParent.normalize();
              }
            }
          }
        }
        return {x: x, y: y};
      }

document.onmouseup = function () {
  var coords = getSelectionCoords();
  document.getElementById("coords").innerHTML = coords.x + ", " + coords.y;
};