Module augmentation syntax in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is module augmentation in TypeScript?

Module augmentation is a way to add new members or modify existing ones in an already declared module without changing the original source code.

beginner

How do you start a module augmentation block in TypeScript?

You use the declare module 'module-name' syntax to open a block where you can add or change module contents.

intermediate

Can you augment a module by adding new functions? Give an example.

Yes. For example, to add a new function <code>newFunc</code> to module <code>myModule</code>:
<pre>declare module 'myModule' {
  export function newFunc(): void;
}</pre>

intermediate

What happens if you augment a module with a conflicting type or member?

TypeScript will merge compatible declarations, but if there is a conflict (like different types for the same member), it will cause a type error.

beginner

Why use module augmentation instead of editing the original module?

Because the original module might be from a library or external source you can't or shouldn't change. Augmentation lets you safely extend it.

Which keyword starts a module augmentation block in TypeScript?

A extend

B module

C declare

D augment

You start with declare module 'module-name' to augment a module.

What is the main purpose of module augmentation?

A To delete members from a module

B To create a new module

C To rename a module

D To add or modify members in an existing module

Module augmentation lets you add or change members in an existing module.

If you add a new function in module augmentation, what must you do?

A Only declare the function signature in the augmentation block

B Delete the original function

C Implement the function inside the augmentation block

D Nothing, it works automatically

You declare the function signature in augmentation; implementation is elsewhere.

What happens if two augmentations declare the same member with different types?

A TypeScript throws a type error

B TypeScript merges them without error

C The last declaration overwrites the first silently

D The compiler ignores the conflict

Conflicting types cause a type error in TypeScript.

Which scenario is best suited for module augmentation?

A Changing core library code directly

B Extending third-party library types safely

C Creating brand new modules

D Deleting unused code

Module augmentation is ideal for safely extending third-party libraries.

Explain how to use module augmentation syntax to add a new function to an existing module.

Think about how you tell TypeScript about new parts without changing original code.

Describe what happens when conflicting types are declared in module augmentation and how to avoid it.

Conflicts cause errors; be careful to match or extend types properly.