function isMatchEmoji($str)
    {
        $pattern='/./u';
        $rs=preg_match_all($pattern,$str,$match);
        if($rs>0){
            foreach($match[0] as $m){
                if(strlen($m) >= 4){
                    return true;
                }
            }            
        }
        return false;
    }
    
    function filter_Emoji($str)
    {
        $str = preg_replace_callback(    //执行一个正则表达式搜索并且使用一个回调进行替换
                '/./u',
                function (array $match) {
                    return strlen($match[0]) >= 4 ? '' : $match[0];
                },
                $str);
     
         return $str;
     }
    
    $str='ko哈罗';
    $rs=isMatchEmoji($str);
    echo $rs?'have emoji':'not have emoji';
    echo filter_Emoji($str);