A 7KB and 0 dependencies AWS Lambda library which supports middleware and easy debug.

Micro AWS Lambda

Intro

• Ready to go Lambda Proxy library
• Written in Typescript
• Zero runtime dependencies
• Tiny: 7KB after minified
• Extendable with middlewares
  • before (handler) hooks
  • after (handler) hooks
  • early exit for just throw httpError() or anything
  • pass values among middlewares
• Return response
  • an object, it will be converted to a Lambda compatible response
  • a customizable httpResponse() / success()
  • a customizable httpError() / badRequest() / internalError()
  • or string, number, boolean
• Easy debug:
  • Adding debug info to response object
  • console.log event / context

Usage

1. Install

npm install micro-aws-lambda

2. Quick start

import { Middleware, lambdaWrapper } from 'micro-aws-lambda';

const lambda: Middleware = ({event, context, passDownObj}) => {}

const handler = lambdaWrapper({
  handler: lambda,
  beforeHooks: [],
  afterHooks: [],
  config: {
      addTraceInfoToResponse: false;
      logRequestInfo: false;
  }
});

• The execution order is: beforeHooks -> handler -> afterHooks .
• beforeHooks , handler , afterHooks all have the same signature:

type Middleware = ({
  event,
  context,
  passDownObj,
}: MiddlewareParams) =>
  | string
  | number
  | boolean
  | PlainObject
  | APIGatewayProxyResult
  | Promise<PlainObject | APIGatewayProxyResult>
  | HttpError
  | HttpResponse
  | void;

event and context is immutable, if you want to pass any info down, attach it to the passDownObj as a property, like passDownObj.value = { message: 'checked' } , the passDownObj object is mutable.

3. Simple handler

Writing an API which will return a JSON and logging things like APIGatewayID and CloudWatchID , blah blah

import { lambdaWrapper, Middleware } from 'micro-aws-lambda';

const lambda: Middleware = ({ event, context, passDownObj }) => {
  return {
    message: 'it works',
  };
};

const handler = lambdaWrapper({
  handler: lambda,
});

// call the API, you will get json response: {message: ""it works"}

4. Before hooks

What about I want to validate this request before executing my lambda? Easy, you just add a hook.

In the following case, if the request name is 'albert', only validateRequest will be called.

import { badRequest } from 'micro-aws-lambda';

const validateRequest: Middleware = ({ event }) => {
  if (event.request.name === 'albert') {
    throw badRequest({
      message: 'bad user, bye bye',
    });
  }
};

const handler = lambdaWrapper({
  // adding to the array
  // omitting the other things for briefing
  beforeHooks: [validateRequest],
});

5. After hooks

You can add afterHooks as well for changing response. The following handler will only return { message: 'bad user, bye bye' } Every middleware in the afterHooks array will receive an additional response as the response.

import { badRequest } from 'micro-aws-lambda';

const validateResponse: Middleware = ({ response }) => {
  if (response?.name === 'albert') {
    throw badRequest({
      message: 'bad user, bye bye',
    };
  })
};

const testHandler = lambdaWrapper({
  handler: () => ({
    name: 'albert',
  }),
  afterHooks: [validateResponse],
});

6. Response

There are 2 types for response, httpError() for throw , and httpResponse() for return , each one of them has some shortcuts to use.

import { httpError, httpResponse } from 'micro-aws-lambda';

// It gives you an instance of HttpError, which extends from Error
const error = httpError({
  // default status code is 400 if not set
  statusCode: 401,
  body: {
    message: 'test',
  },
  headers: {
    'x-http-header': 'fake-header',
  },
});

// It gives you a plain JS object.
const response = httpResponse({
  // default status code is 200 if not set
  statusCode: 200,
  body: {
    message: 'test',
  },
  headers: {
    'x-http-header': 'fake-header',
  },
});

The commons headers are:

• 'Access-Control-Allow-Origin': '*',
• 'Access-Control-Allow-Credentials': true,
• 'Content-Type': 'application/json',

Supports multiValueHeaders and isBase64Encoded in case you need them.

6.1. Shortcuts

Compare to the above methods, the only difference is the shortcuts just sets the status code, you can still modify them if you want.

• httpError :

  badRequest()
  internalRequest()
  

• httpResponse :
  • success() : 200

7. Config

7.1 addTraceInfoToResponse

It will add debug info into the response object

{
  debug: {
    endpoint: "",
    requestBody: "",
    requestMethod: "",

    country: "",
    lambdaRequestId: "",
    logStreamName: "",
    logGroupName: "",
    apiGatewayId: ""
  }
}

7.2 logRequestInfo

It will console.log :

event
context
Aws-Api-Gateway-Request-Id
Identity-Source-Ip

8. Credits

This project was bootstrapped with TSDX .