Function defaultTypeResolver

packages/executor/src/execution/execute.ts:1513–1551

(
  value,
  contextValue,
  info,
  abstractType,
)

 * isTypeOf for the object being coerced, returning the first type that matches.
 */
export const defaultTypeResolver: GraphQLTypeResolver<unknown, unknown> = function (
  value,
  contextValue,
  info,
  abstractType,
) {
  // First, look for `__typename`.
  if (isObjectLike(value) && typeof value['__typename'] === 'string') {
    return value['__typename'];
  }

  // Otherwise, test each possible type.
  const possibleTypes = info.schema.getPossibleTypes(abstractType);
  const promisedIsTypeOfResults: any[] = [];

  for (let i = 0; i < possibleTypes.length; i++) {
    const type = possibleTypes[i];

    if (type.isTypeOf) {
      const isTypeOfResult = type.isTypeOf(value, contextValue, info);

      if (isPromise(isTypeOfResult)) {
        promisedIsTypeOfResults[i] = isTypeOfResult;
      } else if (isTypeOfResult) {
        return type.name;
      }
    }
  }

  if (promisedIsTypeOfResults.length) {
    return Promise.all(promisedIsTypeOfResults).then(isTypeOfResults => {
      for (let i = 0; i < isTypeOfResults.length; i++) {
        if (isTypeOfResults[i]) {
          return possibleTypes[i].name;
        }
      }
    });
  }
};

/**
 * If a resolve function is not given, then a default resolve behavior is used