i found an answer on here, hope can help you
function getCaretCharacterOffsetWithin(element) {
var caretOffset = 0;
var doc = element.ownerDocument || element.document;
var win = doc.defaultView || doc.parentWindow;
var sel;
if (typeof win.getSelection != "undefined") {
sel = win.getSelection();
if (sel.rangeCount > 0) {
var range = win.getSelection().getRangeAt(0);
var preCaretRange = range.cloneRange();
preCaretRange.selectNodeContents(element);
preCaretRange.setEnd(range.endContainer, range.endOffset);
caretOffset = preCaretRange.toString().length;
}
} else if ((sel = doc.selection) && sel.type != "Control") {
var textRange = sel.createRange();
var preCaretTextRange = doc.body.createTextRange();
preCaretTextRange.moveToElementText(element);
preCaretTextRange.setEndPoint("EndToEnd", textRange);
caretOffset = preCaretTextRange.text.length;
}
return caretOffset;
}
function getCaretPosition() {
if (window.getSelection && window.getSelection().getRangeAt) {
var range = window.getSelection().getRangeAt(0);
var selectedObj = window.getSelection();
var rangeCount = 0;
var childNodes = selectedObj.anchorNode.parentNode.childNodes;
for (var i = 0; i < childNodes.length; i++) {
if (childNodes[i] == selectedObj.anchorNode) {
break;
}
if (childNodes[i].outerHTML)
rangeCount += childNodes[i].outerHTML.length;
else if (childNodes[i].nodeType == 3) {
rangeCount += childNodes[i].textContent.length;
}
}
return range.startOffset + rangeCount;
}
return -1;
}
function showCaretPos() {
var el = document.getElementById("test");
var caretPosEl = document.getElementById("caretPos");
caretPosEl.innerHTML = "Caret position: " + getCaretPosition(); //getCaretCharacterOffsetWithin(el);
}
document.body.onkeyup = showCaretPos;
document.body.onmouseup = showCaretPos;
https://codepen.io/neoux/pen/OVzMor