cleaned up version of getUserbyEmail as seen here: https://gajus.medium.com/how-would-you-reduce-nesting-in-this-example-http-gajus-com-blog-8-using-mysql-in-node-js-4c8c71c3a59d

getUserbyEmail.js

// 1. move queries to their own variables

const userQ = 'SELECT `id` FROM `user` WHERE `email` = ?'
const permissionsQ = 'SELECT `id`, `name` FROM `permission` WHERE `user_id` = ?'

// 2. remove codeblocks/explicit return statements
// 3. use 2 spaces instead of 4 for tabs
// 4. leverage ternary operator for that check

const getUserByEmail = (connection, userEmail) => connection
  .queryAsync(userQ, [userEmail])
	.spread(user => user === undefined // reverse the logic
		? {} // i favor an empty object over null
		: connection.queryAsync(permissionsQ, [user.id])
			.then(permissions => ({ ...user, permissions })) // object literal property shorthand was introduced in es6