This is a lambda to handle an api beta tester landing registration in a table.

lambda_email_registration_endpoint.js

const AWS = require('aws-sdk');

//Define aws region
AWS.config.update({
	region:'us-east-1'
});

const TABLE = 'landing_page_emails';

//Get aws dynamo client instance.
const docClient = new AWS.DynamoDB.DocumentClient();

//Register data in dynamodb table.
const addElement = (TableName,element)=>{

  //Create params.
  const params = {
    TableName,
    Item: element
  };

  return docClient.put(params).promise();

}

//DynamoDB find items.
const findEmail = (email) => {

	const params = {
	    TableName: TABLE,
	    FilterExpression: "#email_field = :email_val",
	    ExpressionAttributeNames: {
	        "#email_field": "email",
	    },
	    ExpressionAttributeValues: { ":email_val": email }
	
	};

  //Run query as promise.
  return docClient.scan(params).promise();

}

//Detect if the email is duplicated.
const isDuplicated = async(email)=>{

	//Find email in the BD.
	const found = await findEmail(email);

	//Detect if is duplicated.
	return (found && found.Items && found.Items.length > 0);

}

//Save the email, create user randomly.
const saveEmail = async (email)=>{

	const emailObj = {
		user_id: `beta-${new Date().getTime()}`,
		email
	};

	//Record in the bd.
	return await addElement(TABLE,emailObj);

}

//Validate email string.
const validateEmail = (email)=>{
    const re = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
    return re.test(String(email).toLowerCase());
}

//Make a generic error api builder.
const errorFormatter = (error)=>{

	return {
		statusCode: (error&&error.statusCode)?error.statusCode:500,
		body:JSON.stringify({
			message:(error&&error.message)?error.message:'Internal error'
		})
	};

}

//Lambda handler.
const emailHandler = async (event,context) => {

	try{

		const {
			body
		} = event;

		//Validate body.
		if (!body)
			throw {statusCode:400, message:'Bad request format'};

		const {
			email
		} = JSON.parse(body);

		//Validate email format.
		if (!(email&&validateEmail(email)))
			throw {statusCode:400, message:'Wrong email format'};

		//Detect if is duplicated.
		if (await isDuplicated(email))
			throw {statusCode:406, message:'Email alredy registered'};

		console.info('Registration request', event.body);

		//Record in the table.
		const saved = await saveEmail(email);

		return {
			statusCode:200,
			body:JSON.stringify({
				email,
				message:"Email registered OK"
			})
		};		

	} catch(error){

		console.error('ERROR',error);
		return errorFormatter(error);

	}

};

exports.handler = emailHandler;