Type Guards

Summary

Runtime checks (`typeof`, `instanceof`, custom predicate functions) that let TypeScript narrow a broader type down to a more specific one within a code branch.

How to Learn This

1Write a custom type guard function (`function isX(val): val is X`).
2Practice narrowing a union type inside an `if` block and see the type change.
3Learn the `in` operator as a type guard for checking object properties.

Utility Types

Mapped Types

More topics in TypeScript

Types Interfaces Enums Generics Union Intersection Utility Types Mapped Types Modules Advanced Types React + TS

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