Subscribe a person to a Mailchimp list using an Azure serverless Function App

azure-mailchimp-subscribe.js

/**
 * Expected query parameters via GET or POST
 *
 * email: a valid email address
 * firstName: the first name
 * lastName: the persons last name
 *
 * Don't forget to replace the API key and List ID.
 */
// Add the https://docs.microsoft.com/en-us/azure/azure-functions/functions-reference-node
const MailchimpApi = require('mailchimp-api-v3')
// Add your mailchimp API Key
const mailchimp = new MailchimpApi('API-KEY-GOES-HERE')
// Set the ID for the list people will subscribe to.
const listId = '1234567'

module.exports = function (context, req) {
    context.log('JavaScript HTTP trigger function processed a request.')

    let errorMessage = false

    // Set fields based on GET query or POST body.
    const fields = (req.query || req.body)

    // Set error message if fields are missing
    if (!fields.email) {
        errorMessage = "Oops! Looks like you forgot to add a valid email address."
    }
    else if (!fields.firstName || !fields.lastName) {
        errorMessage = "Please provide a First and Last Name."
    }

    // Exit if there is an error message.
    if (errorMessage) {
        context.res = {
            status: 400,
            body: {
                msg: errorMessage
            }
        }
        
        context.done()
        return
    }

    // Create the data we plan to send to Mailchimp.
    const postDate = {
        "email_address": fields.email,
        "status": "subscribed",
        "merge_fields": {
            "FNAME": fields.firstName,
            "LNAME": fields.lastName
        }
    }

    // Send request to Mailchimp.
    context.log('start request')
    mailchimp.post('/lists/' + listId + '/members', postDate)
        .then(function(results) {
            context.res = {
                body: {
                    response: 'success',
                    msg: "Excellent! Your email address has successfully been added to our Newsletter."
                }
            }
            context.done()
        })
        .catch(function (err) {
            // Log the error.
            context.log(err)
            context.res = {
                status: err.status,
                body: {
                    msg: err.detail
                }
            }
            context.done()
        })

};