middy-middleware-json-error-handler/README.md

A middy JSON error handler middleware.

# middy-middleware-json-error-handler

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A [middy](https://github.com/middyjs/middy) middleware that returns errors as http errors, compatible with [http-errors](https://www.npmjs.com/package/http-errors).

## Installation
Download node at [nodejs.org](http://nodejs.org) and install it, if you haven't already.

```sh
npm install middy-middleware-json-error-handler --save
```

## Documentation

There is [additional documentation](https://dbartholomae.github.com/middy-middleware-json-error-handler).

## Usage

```typescript
import middy from '@middy/core'
import JSONErrorHandlerMiddleware from 'middy-middleware-json-error-handler'
import createHttpError from 'http-errors'
import { APIGatewayEvent } from 'aws-lambda'

// This is your AWS handler
async function helloWorld (event: APIGatewayEvent) {
  if (event.queryStringParameters?.search == null) {
    // If you throw an error with status code, the error will be returned as stringified JSON.
    // Only the stack will be omitted.
    throw createHttpError(400, 'Query has to include a search')
  }

  if (event.queryStringParameters?.search === 'error') {
    // If you throw an error with status code greater than 500 and specify in options that the error
    // must be exposed, then the error will be returned as stringified JSON
    throw createHttpError(500, 'Something went wrong', { expose: true })
  }

  // If you throw an error with no status code, only a generic message will be shown to the user
  // instead of the full error
  throw new Error('Search is not implemented yet')
}

// Specify which are the error properties to omit in response (by default, only the stack is omitted)
const options = {
  errorPropertiesToOmit: ['name', 'statusCode', 'stack']
}

// Let's "middyfy" our handler, then we will be able to attach middlewares to it (options parameter is optional)
export const handler = middy(helloWorld)
  .use(JSONErrorHandlerMiddleware(options)) // This middleware is needed do handle the errors thrown by the handler
```