Typescript's Most Misunderstood Feature: Unions and Intersections

Unions and Intersections in Typescript. A simple topic, right? That's what I thought until I started noticing several conflicting explanations. So I dug in to find the answers myself. Typescript type challenges: https://github.com/type-challenges/type-challenges Iván Ovejero, I have no idea who you are, but thank you for your presentation, which put me on the right trail: https://www.youtube.com/watch?v=JiLoWPwhTf0&ab_channel=Prisma Timecodes 0:00 - Intro 0:32 - The confusion 1:10 - Type Theory: Wikipedia deep dive 3:21 - Sum and Product Type 4:10 - "Union" code example 7:10 - "User Land" and "Type Land" 9:44 - It's not OR, it's BOTH 11:24 - Narrowing the type 12:58 - What about intersections? 14:12 - The inverse relationship 16:37 - We're all going to die