Technologies Coding Problems Bookmarks Learning Paths

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What are type aliases? | Type aliases | typescript Interview Questions | NextRound.in

Questions

1 of 3

1What are type aliases?

2How do you define types in TypeScript?

3How to extend types?

typescript

Commands and Packages

01 / 03

What are type aliases?

Difficulty: 5/10

type alias syntax, union/intersection types, type alias vs interface

We’ve been using object types and union types by writing them directly in type annotations. This is convenient, but it’s common to want to use the same type more than once and refer to it by a single name. It is a name for any type. You can use a type alias to give a name to any type, not just an object type.

ID is a type alias:

Scenario Questions

0-2 years experience

1We have a function that takes a user object with id and name. How would you create a type alias for that shape and use it in the function signature?
2If you rename a type alias that's used across several files, what steps would you take to ensure the code still compiles?
3What happens if you try to assign a string value to a variable declared with a type alias that represents number?

2-5 years experience

Follow-up Questions

Can you walk me through the steps you’d take to rename a type alias across a codebase?
What trade‑offs do you see between using a type alias and an interface in this scenario?
How would you ensure backward compatibility when evolving a shared alias?

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1You need to model a response that can be either a success object with data or an error object with message. How would you use type aliases to represent this union, and what pitfalls might you encounter when extending it later?
2During a refactor, a colleague changed a type alias that was used in a generic utility function, causing a type error elsewhere. How would you debug the issue and decide whether to keep the alias or switch to an interface?
3Explain why using a type alias for a function signature might be preferable in a codebase with many higher‑order functions.

5-8 years experience

1Our codebase has a large set of API request/response types that are repeated across services. How would you design a reusable type alias strategy to avoid duplication while keeping compile times reasonable?
2When dealing with recursive data structures like a tree node, what are the limitations of type aliases versus interfaces, and how would you work around them in a performance‑critical component?
3If a type alias becomes a source of circular reference errors during build, how would you restructure the types to break the cycle without losing type safety?

8+ years experience

1We are planning a migration from a legacy JavaScript codebase to TypeScript. How would you introduce type aliases for shared domain models across multiple teams while minimizing disruption?
2In a micro‑services architecture, several services share common data contracts. What governance model would you propose for maintaining type aliases centrally, and how would you handle versioning and backward compatibility?
3Consider a scenario where a type alias is used in public API typings consumed by external partners. How would you evolve the alias over time without causing breaking changes for those partners?