$.fn.setCursorPosition = function(position){
   if(this.lengh == 0) return this;
   return $(this).setSelection(position, position);
}

$.fn.setSelection = function(selectionStart, selectionEnd) {
   if(this.lengh == 0) return this;
   input = this[0];

   if (input.createTextRange) {
      var range = input.createTextRange();
      range.collapse(true);
      range.moveEnd(‘character‘, selectionEnd);
      range.moveStart(‘character‘, selectionStart);
      range.select();
   } else if (input.setSelectionRange) {
      input.focus();
      input.setSelectionRange(selectionStart, selectionEnd);
   }

   return this;
}

$.fn.focusEnd = function(){
   this.setCursorPosition(this.val().length);
}

$("###").focusEnd();

input框focusEnd