Route parameters in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing a route with parameters?

Consider this NestJS controller method:

  @Get('user/:id')
  getUser(@Param('id') id: string) {
    return `User ID is ${id}`;
  }

What will be the response body when a client requests /user/42?

A "User ID is user/42"

B "User ID is :id"

C "User ID is 42"

D "User ID is undefined"

💡 Hint

Route parameters are extracted from the URL and passed to the method.

The @Param('id') decorator extracts the 'id' part from the URL path. So when the URL is /user/42, id equals '42'. The method returns the string with that value.

📝 Syntax

intermediate

Which option correctly defines a route with two parameters?

You want to create a GET route in NestJS that matches URLs like /order/123/item/456 and extracts both orderId and itemId as parameters.
Which method signature is correct?

A

@Get('order/:orderId/item/:itemId')
getOrderItem(@Param('orderId') orderId: string, itemId: string) { return {orderId, itemId}; }

B

@Get('order/:orderId/item/:itemId')
getOrderItem(@Param() params: {orderId: string, itemId: string}) { return params; }

C

@Get('order/:orderId/item/:itemId')
getOrderItem(@Param('orderId', 'itemId') ids: string[]) { return ids; }

D

@Get('order/:orderId/item/:itemId')
getOrderItem(@Param('orderId') orderId: string, @Param('itemId') itemId: string) { return {orderId, itemId}; }

💡 Hint

Each parameter must be decorated separately or use @Param() to get all.

Option D correctly uses @Param('orderId') and @Param('itemId') to extract each parameter individually. Option D is invalid because @Param() returns an object but the type annotation is incorrect. Option D uses invalid syntax for @Param. Option D misses @Param on itemId.

🔧 Debug

advanced

Why does this route parameter extraction fail?

Given this controller method:

@Get('product/:id')
getProduct(@Param() id: string) {
  return `Product ID: ${id}`;
}

What error or issue will occur when calling /product/10?

A TypeError because id is an object, not a string

B Returns 'Product ID: 10' correctly

C SyntaxError due to missing colon in route

D Runtime error because @Param() is missing argument

💡 Hint

Check what @Param() returns when no argument is given.

@Param() without an argument returns an object with all parameters. Assigning it to a string variable causes a type mismatch. Using it as a string causes a TypeError.

🧠 Conceptual

advanced

How does NestJS handle optional route parameters?

You want to define a route where the parameter category is optional, matching both /products and /products/electronics.
Which route path correctly supports this?

A @Get('products/(category)')

B @Get('products/:category?')

C @Get('products/:category')

D @Get('products/:category*')

💡 Hint

Optional parameters use a question mark in the path.

In NestJS (and Express), adding a question mark after a parameter makes it optional. So ':category?' matches zero or one segment. Other options are invalid syntax or mean different things.

❓ state_output

expert

What is the output of this controller with nested route parameters?

Given this NestJS controller snippet:

@Controller('users')
export class UserController {
  @Get(':userId/posts/:postId')
  getPost(@Param() params: { userId: string; postId: string }) {
    return `User ${params.userId} Post ${params.postId}`;
  }
}

What is the response body when a client requests /users/7/posts/15?

A "User 7 Post 15"

B "User :userId Post :postId"

C "User 7 Post :postId"

D "User undefined Post undefined"

💡 Hint

The @Param() decorator without argument returns an object with all parameters.

The params object contains userId and postId extracted from the URL. So the returned string uses those values correctly.