Guard interface (canActivate) in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the canActivate method in a NestJS guard?

The canActivate method decides if a request can proceed to the route handler. It returns true to allow or false to block access.

beginner

How do you implement a guard using the canActivate method in NestJS?

Create a class that implements the <code>CanActivate</code> interface and define the <code>canActivate(context: ExecutionContext)</code> method to return a boolean, Promise<boolean>, or Observable<boolean>.

intermediate

What does the ExecutionContext parameter provide inside canActivate?

It gives access to details about the current request, like the HTTP request object, handler, and class, so you can check user info or request data.

intermediate

Can canActivate return asynchronous results? How?

Yes, it can return a Promise<boolean> or an Observable<boolean>. NestJS will wait for the result before allowing or blocking access.

beginner

Where do you apply a guard that uses canActivate in a NestJS app?

You can apply it at the controller level, route handler level, or globally to protect routes by adding the guard with decorators or in the app module.

What should the canActivate method return to allow access to a route?

A false

B null

C true

D undefined

Returning true means the guard allows the request to proceed.

Which interface must a guard class implement to use canActivate?

A PipeTransform

B CanDeactivate

C OnModuleInit

D CanActivate

The CanActivate interface requires the canActivate method.

What does the ExecutionContext NOT provide inside canActivate?

A Access to the database connection

B Access to the route handler

C Access to the HTTP request

D Access to the controller class

ExecutionContext does not provide direct access to the database connection.

Can canActivate return an Observable<boolean>?

A Yes

B No

C Only if wrapped in a Promise

D Only if synchronous

NestJS supports returning an Observable from canActivate.

Where can you apply a guard in a NestJS application?

A Only on route handlers

B On controllers, route handlers, or globally

C Only globally

D Only in middleware

Guards can be applied at multiple levels: controller, route handler, or globally.

Explain how the canActivate method works in a NestJS guard and what it controls.

Think about how guards decide if a user can enter a page.

Describe how you would create and apply a simple guard using canActivate in a NestJS app.

Imagine you want to block or allow users based on a rule.