Attach cors header on AWS Lambda (nodejs8.10)

cors.js

module.exports = (response) => {
  const {headers, ...rest} = response
  return {
    ...rest,
    headers: {
      'Access-Control-Allow-Origin': '*',
      ...headers
    }
  }
}

handler.js

const cors = require('./cors')

module.exports.hello = (event, context, callback) => {
  const response = {
    statusCode: 200,
    body: JSON.stringify({
      msg: 'hello, world!'
    })
  }

  callback(null, cors(response))
}