input禁止輸入特殊字符

var tag//目標元素

$(document).on("keydown",tag,function showKeyPress(evt) {
 evt = (evt) ? evt : window.event
 return checkSpecificKey(evt.keyCode);
})

function checkSpecificKey(keyCode) {
    var specialKey = "#$%\^*\'\"\+";//Specific Key list
    var realkey = String.fromCharCode(keyCode);
    var flg = false;
 flg = (specialKey.indexOf(realkey) >= 0);
  if (flg) {
        alert('請勿輸入特殊字符: ' + realkey);
        return false;
    }
    return true;
}