Troubleshooting Handbook: Operators

• typeof and instanceof: type query used for refinement
• keyof: get keys of an object. keyof T is an operator to tell you what values of k can be used for obj[k].
  • Some misconceptions here.
• O[K]: property lookup
• [K in O]: mapped types
• + or - or readonly or ?: addition and subtraction and readonly and optional modifiers
• x ? Y : Z: Conditional types for generic types, type aliases, function parameter types
• !: Nonnull assertion for nullable types
• =: Generic type parameter default for generic types
• as: type assertion
• is: type guard for function return types

Conditional Types are a difficult topic to get around so here are some extra resources:

• fully walked through explanation https://artsy.github.io/blog/2018/11/21/conditional-types-in-typescript/
• Bailing out and other advanced topics https://github.com/sw-yx/ts-spec/blob/master/conditional-types.md
• Basarat's video https://www.youtube.com/watch?v=SbVgPQDealg&list=PLYvdvJlnTOjF6aJsWWAt7kZRJvzw-en8B&index=2&t=0s
• Generics, Conditional types and Mapped types