Bagaimanakah Saya Boleh Menggunakan jQuery untuk Menetapkan Kedudukan Kursor dalam Kawasan Teks?

new function($) {
  $.fn.setCursorPosition = function(pos) {
    if (this.setSelectionRange) {
      this.setSelectionRange(pos, pos);
    } else if (this.createTextRange) {
      var range = this.createTextRange();
      range.collapse(true);
      if (pos < 0) {
        pos = $(this).val().length + pos;
      }
      range.moveEnd('character', pos);
      range.moveStart('character', pos);
      range.select();
    }
  };
}(jQuery);

$('#input').focus(function() {
  $(this).setCursorPosition(4);
});

$.fn.selectRange = function(start, end) {
  if (end === undefined) {
      end = start;
  }
  return this.each(function() {
      if ('selectionStart' in this) {
          this.selectionStart = start;
          this.selectionEnd = end;
      } else if (this.setSelectionRange) {
          this.setSelectionRange(start, end);
      } else if (this.createTextRange) {
          var range = this.createTextRange();
          range.collapse(true);
          range.moveEnd('character', end);
          range.moveStart('character', start);
          range.select();
      }
  });
};

$('#elem').selectRange(3, 5); // select a range of text
$('#elem').selectRange(3); // set cursor position