backend-sendgrid.js

import {fetch} from 'wix-fetch';
import sgMail from '@sendgrid/mail';

var api_key = 'XXXXXX';

export function bufferEncode(url, email, subject, body, filename, filetype) {
    return createBuffer(url)
    .then( (buf) => {
        return sendEmail(buf, email, subject, body, filename, filetype);
    });
}

const createBuffer = (url) => {
	return fetch(url, {
		method: 'GET',
		encoding: null
	})
	.then( (res) => {
		return res.buffer();
	});
}

const sendEmail = async(buffer, email, subject, body, filename, filetype) => {
    let encoded = await encoder(buffer);
    await sgMail.setApiKey(api_key);
    const msg = {
        to: email,
        from: 'Business Name <no-reply@domain.com>',
        subject: subject,
        html: body,
        attachments: [{
            content: encoded,
            filename: filename + '.' + filetype,
            type: 'plain/text',
            disposition: 'attachment',
            contentId: 'mytext'
        }]
    };
    sgMail.send(msg)
    .then( function (err, response) {
        if(err){
            return Promise.resolve(err);
        }else{
            return Promise.resolve(response);
        }
    })
    .catch( (err) => {
        return Promise.resolve(err);
    });
}

const encoder = (string) => {
	var encryptedBytes = Buffer.from(string);
    var encoded = encryptedBytes.toString('base64');
	return encoded;
}