Learning Typescript was probably one of the best investments of time I have ever made. It took like 3 hours to learn all together and saved me at least 20 hours of debugging already.
Me, raising an incredulous eyebrow.
If you already know JS I really think you could learn 80% of TypeScript in three hours. But the last 20% would take a long time: generics, union types, that sort of stuff.
The harder parts are the advanced types which you can learn middle out as you go.
Still not rocket science, but it takes way more than 3 hours, even if one studies it intensively.