Function overloads

Last reviewed May 28, 2026 Content v20260528

Track mode

client_typescript

Means

In-browser TS

Reading

~1 min

Level

intermediate

This lesson

This lesson teaches Function overloads—the ideas, syntax, and habits you need before moving on in TypeScript.

Without a solid grasp of Function overloads, you will repeat mistakes in TypeScript exercises and on real pages or scripts.

You will apply Function overloads in contexts like: Modern front-end apps, Node APIs, and any team that standardizes on TS-first tooling.

Write TypeScript, compile in the browser, run the emitted JavaScript, and check understanding with MCQs.

When the previous lesson's MCQs feel easy and you can explain Function overloads in your own words.

Overload signatures describe call shapes; one implementation signature must be compatible with all overloads.

Implementation signature

Callers see overloads; the implementation must accept the union of all cases. Keep overload sets small—large sets often mean a single options object is clearer.

Self-check

Write two overloads for formatDate(date: Date): string and formatDate(ts: number): string.

In code review, prefer a single options object when overload count grows past two or three signatures.

Practice: Apply function-overloads in the playground, then explain function overloads in one sentence without looking at notes.

Playground

Runs in your browser in a sandboxed frame. Backend runners appear when this track’s profile allows them.

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