code: function decode(string, tag) {
  
      tag = tag || '\\u';
  
      var newString = '';
      var open = false;
      var char, charCode;
      var index = -1;
      var length = string.length;
      while (++index < length) {
          char = string.charAt(index);
          charCode = char.charCodeAt(0);
          if (open) {
              if (char === tag) {
                  newString += tag;
              } else {
                  var hex = parseInt(string.substr(index, 4), 16);
                  if (isNaN(hex)) {
                      newString += char;
                  } else {
                      newString += String.fromCharCode(hex);
                      index += 3;
                  }
              }
              open = false;
          } else {
              if (char === tag) {
                  open = true;
              } else {
                  newString += char;
              }
          }
      }
  
      return newString;
  
  }
docs: unicode 字符串解码
  @see http://andyyou.github.io/javascript/2015/05/21/js-unicode-issue.html
  @param   {String}
  @param   {String}    编码开始标记，默认`\u`