Basic Lambda to serve POST request

express.js

import express from 'express';
import cors from 'cors';
import handler from './lambda';
import lambdaToExpress from './lambda-to-express';

const PORT = 3000;
const app = express();

app.use(cors());
app.use(express.json()); // Parse JSON bodies

app.put('/lead/:leadId', lambdaToExpress(handler));

app.listen(PORT);

lambda-to-express.js

// Convert from a Lambda to an ExpressJS handler
const lambdaToExpress = async (handler) => {
  return async (req, res) => {
    // Repackage the express parameters as an event object for the Lambda
    const event = {
      body: JSON.stringify(req.body),
      headers: req.headers,
      queryStringParameters: req.query,
      pathParameters: req.params
    };

    const handlerRes = await handler(event);

    // Instruct express to use the response from the Lambda 
    res.status(handlerRes.statusCode).json(JSON.parse(handlerRes.body))
  };
}

export default lambdaToExpress;

lambda.js

import leadService from './lead-service';

// Define a handler for `PUT /lead/:leadId` that accepts the request body payload `{ name, email }`
const handler = async (event) => {
  // Parse the request parameters
  const { name, email } = JSON.parse(event.body);
  const { leadId } = event.pathParameters;

  // Assume this is the service-layer code that actually performs the updating of the lead
  await leadService.update(leadId, name, email);

  // Return a 200 success code and the full lead
  return {
    statusCode: 200,
    body: JSON.stringify({
      id: leadId,
      name,
      email
    })
  };
}

export default handler;