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TypeScript Generics

Write reusable code that keeps types.

✍️ 3 exercises + code challenge in this lesson
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Generics let a function or class work with many types while keeping type safety:

function first<T>(items: T[]): T { return items[0]; }

  • TypeScript infers T from the arguments.
  • Constraints limit what T can be: <T extends { length: number }>
  • Generic interfaces and classes: interface Box<T> { value: T }

Key Takeaways: TypeScript Generics

Mastering TypeScript Generics helps you write clean and reliable TypeScript code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

TypeScript Generics Code Example

TypeScript 
function first<T>(items: T[]): T {
  return items[0];
}

function longest<T extends { length: number }>(a: T, b: T): T {
  return a.length >= b.length ? a : b;
}

interface Box<T> {
  value: T;
}

const box: Box<number> = { value: 99 };
console.log(first(["a", "b"]), longest("hello", "hi"), box.value);
Output
a hello 99
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TypeScript Generics Practice Exercises

Check what you learned in “TypeScript Generics”.

/ 3 solved
Fill in the blank

Declare a generic type parameter.

function identity(value: T): T { return value; }
✓ Correct! Not quite. Try again.
Multiple choice

Why use generics?

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Code challenge

Write a generic last<T>(items: T[]): T that returns the last item. Log last([1, 2, 3]).

Write the code in the live editor. Your answer is checked automatically.

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TypeScript Classes
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TypeScript Utility Types

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