docs: function deepFreeze(obj) {
              Object.freeze(obj);
  
              if (obj instanceof Array) {
                  for (var i = 0; i < obj.length; i += 1) {
                      if (obj[i] !== null && typeof obj[i] === 'object') {
                          deepFreeze(obj[i]);
                      }
                  }
              } else {
                  for (var key in obj) {
                      if (obj[key] !== null && typeof obj[key] === 'object') {
                          deepFreeze(obj[key]);
                      }
                  }
              }
          }