Invalid db option causes ReplyError: ERR invalid DB index

[paxcol]

How to reproduce

Pass db option as a string when creating Redis object:

const Redis = require("ioredis");
const redis = new Redis({db: 'some-string'})

It will throw an uncaught error:

(node:2467) UnhandledPromiseRejectionWarning: ReplyError: ERR invalid DB index
    at parseError (node_modules/redis-parser/lib/parser.js:179:12)
    at parseType (node_modules/redis-parser/lib/parser.js:302:14)

(node:2467) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 2)
(node:2467) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

What causes this

All select commands have no callback or error handling in ioredis.

What I expect

This error is caught by ioredis either through a rejected promise fromRedis.connect() or the error event listener but not an unhandledPromiseRejection.

Linked issues

1. ReplyError: ERR invalid DB index #1113
2. ReplyError: ERR invalid DB index  #74