All Challengesintermediate

TypeScript generics basics

Generics appear in almost every TypeScript codebase. AI uses them to write reusable functions.

typescriptgenericstype inferencereusability
typescript
function getFirst<T>(arr: T[]): T | undefined {
  return arr[0]
}

function wrap<T>(value: T): { data: T; timestamp: number } {
  return { data: value, timestamp: Date.now() }
}

const num = getFirst([1, 2, 3])
const str = getFirst(['a', 'b', 'c'])
const empty = getFirst([])

Question

What are the TypeScript types of num, str, and empty?

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