code: function getSingleCallSignature(type) {
              if (type.flags & 2588672 /* ObjectType */) {
                  var resolved = resolveStructuredTypeMembers(type);
                  if (resolved.callSignatures.length === 1 && resolved.constructSignatures.length === 0 &&
                      resolved.properties.length === 0 && !resolved.stringIndexInfo && !resolved.numberIndexInfo) {
                      return resolved.callSignatures[0];
                  }
              }
              return undefined;
          }
docs: If type has a single call signature and no other members, return that signature. Otherwise, return undefined.