What types exist only at compile time in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are types that exist only at compile time in TypeScript?

These are types used by the TypeScript compiler to check code correctness but do not exist in the JavaScript output. They help catch errors before running the code.

beginner

Do TypeScript interfaces exist in the compiled JavaScript code?

No, interfaces are removed during compilation. They only help with type checking while writing code and do not produce any JavaScript code.

beginner

What happens to TypeScript type aliases after compilation?

Type aliases are used only at compile time for type checking and are erased in the compiled JavaScript, so they do not exist at runtime.

intermediate

Are enums in TypeScript compile-time only types?

No, enums generate JavaScript code and exist at runtime. Only types, interfaces, and generics are compile-time only.

intermediate

What is the difference between types/interfaces and classes in TypeScript regarding runtime?

Types and interfaces exist only at compile time and are erased after compilation. Classes produce JavaScript code and exist at runtime.

Which TypeScript construct exists only at compile time?

A Class

B Enum

C Interface

D Function

Interfaces are used only for type checking and do not exist in the compiled JavaScript.

What happens to type aliases after TypeScript compilation?

A They are removed and do not exist at runtime

B They become JavaScript variables

C They become functions

D They become classes

Type aliases are erased during compilation and only help with type checking.

Which of these exists at runtime in JavaScript after compiling TypeScript?

A Type alias

B Enum

C Interface

D Type parameter

Enums generate JavaScript code and exist at runtime.

Are TypeScript generics present in the compiled JavaScript code?

A Yes, as functions

B Yes, as objects

C Yes, as classes

D No, they are compile-time only

Generics are used only for type checking and are removed after compilation.

Which statement is true about TypeScript interfaces?

A They exist only at compile time

B They become JavaScript objects

C They compile to JavaScript classes

D They are runtime types

Interfaces are erased during compilation and only help with type checking.

Explain which TypeScript types exist only at compile time and why.

Think about what TypeScript removes when it creates JavaScript.

Describe the difference between TypeScript types/interfaces and classes regarding runtime presence.

Consider what code actually runs in the browser or Node.js.