js limits form input length. Chinese characters are two characters_form special effects

This effect is integrated into a function. This function accepts 3 parameters:
The first is the ID of the textarea or other text form;
The second is the ID of the displayed input content, which can be left blank;
The third one is the most input character, one Chinese character is 2 characters.
This is just a basic effect, and students are welcome to optimize and improve it.
To get the code, please view the source file of the demo

<meta charset="utf-8"> <title>Limit the form input length to two characters for Chinese characters</title> <meta name="auther" content="f7"> <textarea name="textarea" id="commentText" style="width:500px; height:150px;"> <input type="button" value="JS添加内容" onclick="document.getElementById('commentText').value = '您想说dasdsadsad的话！请输5325135353入您想说的'; lengthLimit('commentText', 'dsa', 40);"> Enter up to 20 Chinese characters <div id="dsa"> </div>
[Ctrl A select all Note:

If you need to introduce external Js, you need to refresh to execute <script> function lengthLimit(elem, showElem, max){ var elem = document.getElementById(elem); var showElem = document.getElementById(showElem); var max = max || 50;// 最大限度字符，汉字按两个字符计算 function getTextLength(str){// 获取字符串的长度 一个汉字为2个字符 return str.replace(/[^\x00-\xff]/g,"xx").length; }; // 监听textarea的内容变化 if(/msie (\d+\.\d)/i.test(navigator.userAgent) == true) {// 区分IE elem.onpropertychange = textChange; }else{ elem.addEventListener("input", textChange, false); } function textChange(){// 内容变化时的处理 var text = elem.value; var count = getTextLength(text); if(count > max){// 文字超出截断 for(var i=0; i<text.length; i++){ if(getTextLength(text.substr(0, i)) >= max){ elem.value = text.substr(0, i); if(showElem) showElem.innerHTML = elem.value;// 显示输出结果 break; }; } }else{ if(showElem) showElem.innerHTML = elem.value;// 显示输出结果 }; }; textChange();// 加载时先初始化 }; </script>]