Using

Provides a convenient syntax that ensures the correct use of Disposable or Destroyable objects. That is, objects with either a dispose() or destroy() methods on them.

This pattern is used primarily to clean up connections to remote resources. For example, the AWS SDK provides .destroy() methods on many of their client classes.

Usage

Call using and for its first argument, pass it a resource or dictionary of resources to be disposed or destroyed after the use context closes. For its second argument, pass a function that will use the provided resources. When this function's scope closes, the using function will automatically call the disposal methods on each resource.

Finally, a third argument can be optionally passed to either change the target disposal method from .dispose() to .destroy() or to enable throwing on errors.

Dispose

By default, using will attempt to call .dispose():

const createCustomer = async (customer: ICustomer) => {
  // Value returned from provided function is returned 
  const createdCustomer = await using(
    new Repository<Customer>(),
    // Type is inferred
    (customerRepository) => {
      return customerRepository.create(customer);
      // customerRepository.dispose() will be automatically called when the scope closes
    },
  );

  return createdCustomer;
};

Destroy

You can optionally specify to call .destroy() instead:

const createCustomer = async (customer: ICustomer) => {
  // Value returned from provided function is returned 
  const createdCustomer = await using(
    new DynamoDBClient(dynamoDbConfig),
    // Type is inferred
    (dynamoDbClient) => {
      const command = new DynamoDbPutCommand({
        TableName: 'customer',
        ... // data, etc
      })
      return dynamoDbClient.send(command);
      // dynamoDbClient.destroy() will be automatically called when the scope closes
    },
    // Must specify key to override default value of 'dispose'
    { key: 'destroy' },
  );

  return createdCustomer;
};

Dictionary

Instead of passing a single resource, you can pass a dictionary of resources and they will all be disposed or destroyed when the function closure exits.

const getUsersFavoriteRecipe = async (userId: string) => {
  // Value returned from provided function is returned
  const favoriteRecipe = await using(
    {
      userRepository: new Repository<User>(),
      recipeRepository: new Repository<Recipe>(),
    },
    async ({
      // Dictionary item types are inferred
      userRepository,
      recipeRepository,
    }) => {
      const user = await userRepository.get(userId);
      return recipeRepository.get(user.favoriteRecipeId);
      // userRepository.dispose() and recipeRepository.dispose() will be automatically called when the scope closes
    }
  );

  return favoriteRecipe;
};

Same as earlier, you can override the key to call .destroy() instead.

throwOnError

You can provide the option throwOnError to throw if the disposing method was not found. This is intended for debugging during development and its use is discouraged in production environments as it will throw immediately and will not dispose remaining items in a dictionary.