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TypeScript in Depth · Generics · Lesson 8 of 16

Generic Functions

Concept

Generic Functions

A generic function's type parameter is inferred from the arguments you pass, or can be specified explicitly.

By the end of this lesson
  • Explain the core idea behind Generic Functions.
  • Predict output before running a change.
  • Test one realistic and one unusual input.
  • Use the result to make the next decision.
How to study this page
  1. 1. Read one concept.
  2. 2. Change the example.
  3. 3. Run, compare, and explain.
  4. 4. Complete the challenge below.
ExampleRunnable
function firstItem<T>(items: T[]): T {
  return items[0];
}
Try it Yourself »
Self-check before continuing

Without looking at the example, describe what changes when you modify one input in Generic Functions. Then reopen the editor and prove your explanation with a small test.

You are ready to continue when you can predict, test, and explain the result.

Your turn

Write a generic function lastItem that returns the last element of any array.

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Console

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