function cutstr(str, len) {    var str_length = 0;    var str_len = 0;    var str_cut = new String();    var str_len = str.length;    for (var i = 0; i < str_len; i++) {        a = str.charAt(i);        str_length++;        if (escape(a).length > 4) {            //中文字符的长度经编码之后大于4            str_length++;        }        str_cut = str_cut.concat(a);        if (str_length >= len) {            str_cut = str_cut.concat("...");            return str_cut;        }    }    //如果给定字符串小于指定长度，则返回源字符串；    if (str_length < len) {        return str;    }}