判断输入文字的个数js

function regInputHandler(docId, len, infoDocId) {
    var doc = document.getElementById(docId);
    doc.onkeyup = checkN;
    checkN.call(doc);
    function checkN() {
        var vv = this.value || '';
        var v = vv.replace(/[^\x00-\xff]/g, "**");
        var keyLen = v.length;
        if (keyLen < len) {
            document.getElementById(infoDocId).innerHTML = "您还可以输入" + (len - keyLen) + "个字符,或您还可以输入" + parseInt((len - keyLen) / 2) + "个汉字"
        } else if (keyLen > len) {
            document.getElementById(infoDocId).innerHTML = "您输入的内容已经达到系统规定的最大字数";
            var txt = '';
            var i = 0;
            while (true) {
                txt += vv.substr(i, 1);
                if (txt.replace(/[^\x00-\xff]/g, "**").length >= len) {
                    if (txt.replace(/[^\x00-\xff]/g, "**").length == len) {
                        this.value = txt
                    } else {
                        this.value = txt.substr(0, txt.length - 1)
                    }
                    break
                }
                i++
            }
            fn.alert('您输入的内容过长')
        } else {
            document.getElementById(infoDocId).innerHTML = "您输入的内容已经达到系统规定的最大字数"
        }
    }
};

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