Add a new contact to a SendGrid contact list using the SendGrid API via a Netlify Typescript Function.

subscribe.ts

import { Handler } from "@netlify/functions"
import client from "@sendgrid/client"
import { ClientRequest } from "@sendgrid/client/src/request"

const blogListId = `0350949f-5c47-4bb3-b8fb-83e848f9d8ae`

const handler: Handler = async (event, context) => {
  if (event.httpMethod !== `POST`) {
    return {
      statusCode: 405,
      body: `Method Not Allowed`,
    }
  }

  if (typeof process.env.SENDGRID_TOKEN !== `string`) {
    return {
      statusCode: 500,
      body: `Could not set Sendgrid API Key`,
    }
  }

  client.setApiKey(process.env.SENDGRID_TOKEN)

  let reqBody

  // Check values from frontend
  if (event?.body) {
    reqBody = JSON.parse(event.body)
  }

  if (!reqBody) {
    return {
      statusCode: 400,
      body: `No response body found.`,
    }
  }

  const { firstName, lastName, email } = reqBody

  if (!firstName || !email) {
    return {
      statusCode: 400,
      body: `Please provide an email address and first name`,
    }
  }

  // Fetch marketing mailing list
  const query = {
    query: `email = '${email}' AND CONTAINS(list_ids, '${blogListId}')`,
  }

  const request: ClientRequest = {
    url: `/v3/marketing/contacts/search`,
    method: `POST`,
    body: query,
  }

  let recipients

  try {
    recipients = await client.request(request)
  } catch (e) {
    return {
      statusCode: 500,
      body: `Failed to fetch current mailing list.`,
    }
  }

  // Check if email is already in mailing list
  // If they  are in the list, return an error
  const [response, body] = recipients

  if (!body) {
    return {
      statusCode: 500,
      body: `Could not retreive contact list.`,
    }
  }

  const { contact_count: contactCount, result } = body

  if (contactCount > 0 && result.map((cont: { email: string }) => cont.email).includes(email)) {
    return {
      statusCode: 409,
      body: `User is already subscribed.`,
    }
  }

  // If user is not subscribed, add the new user
  // as a subscriber
  const data = {
    list_ids: [blogListId],
    contacts: [
      {
        first_name: firstName,
        last_name: lastName || ``,
        email,
      },
    ],
  }

  const signupReqConfig: ClientRequest = {
    method: `put`,
    url: `/v3/marketing/contacts`,
    body: data,
  }

  try {
    await client.request(signupReqConfig)

    // Return success status code
    return {
      statusCode: 200,
    }
  } catch (e) {
    return {
      statusCode: 500,
      body: `Server error.`,
    }
  }
}

// eslint-disable-next-line import/prefer-default-export
export { handler }