JavaScript中英文 字符串截取

/**
  * 中英文字符串截取
  * @param str  要截取的字符串
  * @param len  要截取的长度
  * @param hasDot 是否在字符串末尾增加‘...‘
  * @returns {string}
  *
  */
          
function mySubString (str, len, hasDot){
        var newLength = 0;
        var newStr = "";
        var chineseRegex = /[^\x00-\xff]/g;
        var singleChar = "";
        var strLength = str.replace(chineseRegex,"**").length;
        for(var i = 0;i < strLength;i++)     {
          singleChar = str.charAt(i).toString();
          if(singleChar.match(chineseRegex) != null) {
            newLength += 2;
          }else {
            newLength++;
          }
          if(newLength > len) {
            break;
          }
          newStr += singleChar;
        }
        if(hasDot && strLength > len) {
          newStr += "...";
        }
        return newStr;
    }