TypeScript tutorialLesson 27Free preview

TS Type Guards

This lesson is part of TypeScript · All levels

Summary

Type guard is a runtime check that allows the compiler to infer narrower types on a particular block. Operators typeof and instanceof are built-in guards, while custom guards can be written with the return type predicate pattern. This technique is crucial to working safely with the union type.

Key points

Distinguish between primitive
Check the instance class
Predicate v is T tells the compiler the test results

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