如何知道文本区光标是否到达字段的最后？

var input = document.getElementById("myInput");
var selection = window.getSelection();
var cursorPosition = selection.focusOffset;
var fieldLength = input.value.length;

if (cursorPosition === fieldLength) {
  console.log("光标已到达字段的最后");
} else {
  console.log("光标未到达字段的最后");
}

var input = document.getElementById("myInput");
var cursorPosition = getCaretPosition(event.clientX, event.clientY);
var fieldLength = input.value.length;

if (cursorPosition === fieldLength) {
  console.log("光标已到达字段的最后");
} else {
  console.log("光标未到达字段的最后");
}

function getCaretPosition(x, y) {
  var range = document.caretPositionFromPoint(x, y);
  return range.offset;
}

var input = document.getElementById("myInput");
var range = document.selection.createRange();
var cursorPosition = range.text.length;
var fieldLength = input.value.length;

if (cursorPosition === fieldLength) {
  console.log("光标已到达字段的最后");
} else {
  console.log("光标未到达字段的最后");
}