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Type Assertion Safety
basictypescript
Background
Type assertions override TypeScript inferred types and should be used with runtime validation for safety.
Problem
Write a function that takes an unknown value, asserts it is a string after runtime checking, and returns its uppercase version.
Input
A value of type unknown.
Output
An uppercase string if the value is a string, otherwise null.
Sample tests
Sample 1
Input: "hello"
Expected: "HELLO"
Your solution
Learning objective
Learn safe type assertion patterns with runtime validation for unknown values.