在textarea指定位置插入字符或表情

(function($){
 $.fn.extend({
  insertAtCaret: function(myValue){
   var $t=$(this)[0];
   if (document.selection) {
    this.focus();
    sel = document.selection.createRange();
    sel.text = myValue;
    this.focus();
   }
   else
    if ($t.selectionStart || $t.selectionStart == '0') {
     var startPos = $t.selectionStart;
     var endPos = $t.selectionEnd;
     var scrollTop = $t.scrollTop;
     $t.value = $t.value.substring(0, startPos) + myValue + $t.value.substring(endPos, $t.value.length);
     this.focus();
     $t.selectionStart = startPos + myValue.length;
     $t.selectionEnd = startPos + myValue.length;
     $t.scrollTop = scrollTop;
    }
    else {
     this.value += myValue;
     this.focus();
    }
  }
 }) 
})(jQuery);

[代码]调用方法     

1	$("#textareaId").insertAtCaret("新表情");