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appsync-events.md appsync-graphql.md bedrock-agent.md http-middleware.md http-routing.md index.md

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tessl/npm-aws-lambda-powertools--event-handler

Lightweight routing to reduce boilerplate for API Gateway REST/HTTP API, ALB, Lambda Function URLs, and AppSync.

Workspace: tessl
Visibility: Public
Created: 1 day ago
Last updated: 1 day ago
Describes: pkg:npm/@aws-lambda-powertools/event-handler@2.29.x

To install, run

npx @tessl/cli install tessl/npm-aws-lambda-powertools--event-handler@2.29.0

AWS Lambda Powertools Event Handler

Lightweight routing for Lambda functions handling events from API Gateway (REST/HTTP), ALB, Lambda Function URLs, AWS AppSync (GraphQL/Events), and Amazon Bedrock Agents.

Package

Name: @aws-lambda-powertools/event-handler
Type: npm
Language: TypeScript
Install: npm install @aws-lambda-powertools/event-handler

Imports

// HTTP (API Gateway, ALB, Function URLs)
import { Router, HttpStatusCodes, NotFoundError, RouteMatchingError, ParameterValidationError, composeMiddleware } from '@aws-lambda-powertools/event-handler/http';
import { cors, compress } from '@aws-lambda-powertools/event-handler/http/middleware';

// AppSync GraphQL
import { AppSyncGraphQLResolver, makeId, awsDateTime, awsDate, awsTime, awsTimestamp } from '@aws-lambda-powertools/event-handler/appsync-graphql';

// AppSync Events
import { AppSyncEventsResolver, UnauthorizedException } from '@aws-lambda-powertools/event-handler/appsync-events';

// Bedrock Agent
import { BedrockAgentFunctionResolver, BedrockFunctionResponse } from '@aws-lambda-powertools/event-handler/bedrock-agent';

// CommonJS
const { Router } = require('@aws-lambda-powertools/event-handler/http');

Type Inference: TypeScript types are inferred automatically. Most types are not exported as runtime values. Use generic parameters for custom typing.

Quick Start

HTTP Router

import { Router } from '@aws-lambda-powertools/event-handler/http';
const router = new Router();
router.get('/hello', async ({ req }) => ({ message: 'Hello World!' }));
router.post('/users', async ({ req }) => {
  const body = await req.json();
  return new Response(JSON.stringify({ id: '123', ...body }), { status: 201 });
});
export const handler = async (event, context) => router.resolve(event, context);

AppSync GraphQL

import { AppSyncGraphQLResolver } from '@aws-lambda-powertools/event-handler/appsync-graphql';
const app = new AppSyncGraphQLResolver();
app.onQuery<{ id: string }>('getTodo', async ({ id }) => ({ id, title: 'Sample', completed: false }));
app.onMutation<{ title: string }>('createTodo', async ({ title }) => ({ id: makeId(), title, completed: false }));
export const handler = async (event, context) => app.resolve(event, context);

Architecture

Router Classes: Specialized resolver per AWS service (HTTP, AppSync GraphQL, AppSync Events, Bedrock Agent)
Middleware: Composable with onion model execution (HTTP only)
Web Standards: HTTP router uses Web API Request/Response internally
Type Safety: Full TypeScript support with generics
Error Handling: Custom error classes and handlers
Decorators: Optional decorator-based registration

Capabilities

HTTP Routing

API Gateway (V1/V2), ALB, Lambda Function URLs with middleware support.

class Router {
  constructor(options?: { logger?: GenericLogger; prefix?: Path });
  resolve(event, context, options?: ResolveOptions): Promise<APIGatewayProxyResult | APIGatewayProxyStructuredResultV2 | ALBResult>;
  get|post|put|patch|delete|head|options(path: Path, handler: RouteHandler): void;
  get|post|put|patch|delete|head|options(path: Path, middleware: Middleware[], handler: RouteHandler): void;
  use(middleware: Middleware): void;
  includeRouter(router: Router, options?: { prefix: Path }): void;
  errorHandler<T extends Error>(errorType: ErrorConstructor<T> | ErrorConstructor<T>[], handler: ErrorHandler<T>): void;
}

HTTP Middleware

CORS, compression, and custom middleware composition.

cors(options?: CorsOptions): Middleware;
compress(options?: CompressionOptions): Middleware;
composeMiddleware(middleware: Middleware[]): Middleware;

AppSync GraphQL

Route GraphQL queries, mutations, and custom resolvers without VTL.

class AppSyncGraphQLResolver {
  constructor(options?: { logger?: GenericLogger });
  resolve(event, context, options?: ResolveOptions): Promise<unknown>;
  onQuery<TParams>(fieldName: string, handler: ResolverHandler<TParams>): void;
  onMutation<TParams>(fieldName: string, handler: ResolverHandler<TParams>): void;
  resolver<TParams>(handler: ResolverHandler<TParams>, options: { fieldName: string; typeName?: string }): void;
  batchResolver<TParams, TSource>(handler: BatchResolverHandler<TParams, TSource>, options: GraphQlBatchRouteOptions): void;
  exceptionHandler<T extends Error>(error: ErrorClass<T> | ErrorClass<T>[], handler: ExceptionHandler<T>): void;
}

AppSync Events

Real-time pub/sub with automatic channel routing.

class AppSyncEventsResolver {
  constructor(options?: { logger?: GenericLogger });
  resolve(event, context, options?: ResolveOptions): Promise<void | OnPublishOutput | OnPublishAggregateOutput>;
  onPublish<T extends boolean>(path: string, handler: OnPublishHandler<T>, options?: { aggregate?: T }): void;
  onSubscribe(path: string, handler: OnSubscribeHandler): void;
}

Bedrock Agent Functions

Expose tools for LLM agents with automatic routing.

class BedrockAgentFunctionResolver {
  constructor(options?: { logger?: Pick<GenericLogger, 'debug' | 'warn' | 'error'> });
  tool<TParams extends Record<string, ParameterValue>>(fn: ToolFunction<TParams>, config: { name: string; description?: string }): void;
  resolve(event, context): Promise<BedrockAgentFunctionResponse>;
}

Common Types

interface GenericLogger {
  debug(message: string, ...args: unknown[]): void;
  info(message: string, ...args: unknown[]): void;
  warn(message: string, ...args: unknown[]): void;
  error(message: string, ...args: unknown[]): void;
}

interface ResolveOptions {
  scope?: unknown; // For decorator binding
}

type JSONValue = string | number | boolean | null | JSONValue[] | { [key: string]: JSONValue };