input限制字符长度

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>demo</title>
</head>
<body>
    <input id="text" placeHolder="最大支持12个字节" maxlength="12" />
    <script type="text/javascript">
     var Str = {
         byteLen : function (str){
            //正则取到中文的个数，然后len*count+原来的长度。不用replace
            str += '';
            var tmp = str.match(/[^x00-xff]/g) || [];
            return str.length + tmp.length;
        },
        getMaxlen : function(str,maxlen){
            var sResult = '', L=0, i=0, stop = false, sChar;
            if(str.replace(/[^x00-xff]/g,'xxx').length <= maxlen){
                return str;
            }
            while(!stop){
                sChar = str.charAt(i);
                L+= sChar.match(/[^x00-xff]/) ? 2 : 1;
                if(L > maxlen){
                    stop = true;
                }else{
                    sResult+=sChar;
                    i++;
                }
            }
            return sResult;
        }
    };
    var inputLock = false;
    document.querySelector('#text').addEventListener('compositionstart', function(){
        inputLock = true;
    })
    document.querySelector('#text').addEventListener('compositionend', function(){
        inputLock = false;
        var value = this.value,
            maxlength = this.getAttribute('maxlength');
        if(Str.byteLen(value) > maxlength){
            this.value = Str.getMaxlen(value, maxlength);
        }
    })
    document.querySelector('#text').addEventListener('input', function(){
        if(!inputLock){
            var value = this.value,
                maxlength = this.getAttribute('maxlength');
            if(Str.byteLen(value) > maxlength){
                this.value = Str.getMaxlen(value, maxlength);
            }
        }
    });
    </script>
</body>
</html>
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原文地址：https://www.cnblogs.com/jkr666666/p/11173424.html