Query parameters in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this NestJS controller method when called with ?page=3&limit=10?

Consider the following NestJS controller method that reads query parameters:

  @Get('items')
  getItems(@Query('page') page: string, @Query('limit') limit: string) {
    return `Page: ${page}, Limit: ${limit}`;
  }

What will be the response body when a client requests /items?page=3&limit=10?

NestJS

  @Get('items')
  getItems(@Query('page') page: string, @Query('limit') limit: string) {
    return `Page: ${page}, Limit: ${limit}`;
  }

A "Page: 3, Limit: 10"

B "Page: 0, Limit: 0"

C "Page: undefined, Limit: undefined"

D "Page: null, Limit: null"

💡 Hint

Query parameters are passed as strings from the URL and injected by NestJS into the method parameters.

The @Query('param') decorator extracts the query parameter as a string. Since the URL has page=3 and limit=10, these values are passed as strings to the method, resulting in the returned string showing those values.

📝 Syntax

intermediate

Which option correctly extracts all query parameters as an object in NestJS?

In NestJS, you want to get all query parameters as a single object inside a controller method. Which code snippet correctly does this?

A getData(@Query: any query) { return query; }

B getData(@Query('query') query: any) { return query; }

C getData(@Query({}) query) { return query; }

D getData(@Query() query: any) { return query; }

💡 Hint

Use @Query() without parameters to get all query params as an object.

The @Query() decorator without arguments injects all query parameters as an object. Option D correctly uses this syntax. Option D tries to get a parameter named 'query' which is incorrect. Option D and D are invalid syntax.

❓ state_output

advanced

What is the value of 'page' after this controller method runs with URL ?page=5?

Given this NestJS controller method:

  @Get('search')
  search(@Query('page') page: number = 1) {
    return page;
  }

What will be the returned value if the client calls /search?page=5?

NestJS

  @Get('search')
  search(@Query('page') page: number = 1) {
    return page;
  }

A NaN

B "5"

C 1

D 5

💡 Hint

Query parameters are strings by default. TypeScript types do not convert them automatically.

The @Query('page') page: number = 1 declares page as a number in TypeScript, but NestJS injects the query parameter as a string ('5'). TypeScript types do not affect runtime behavior or perform automatic conversion. Thus, page is the string "5", and it is returned as such.

🔧 Debug

advanced

Which option causes a runtime error when accessing query parameters?

Consider these NestJS controller methods. Which one will cause a runtime error when called with /data?filter=active?

A getData(@Query('filter') filter: string) { return filter.toUpperCase(); }

B getData(@Query('filter') filter: string) { return filter.length; }

C getData(@Query('filter') filter: string) { return filter.toFixed(2); }

D getData(@Query('filter') filter: string) { return filter.trim(); }

💡 Hint

Check which string method does not exist or is invalid.

Options A, B, and D call valid string methods. Option C calls toFixed, which is a method for numbers, not strings. Since filter is a string, calling toFixed causes a runtime error.

🧠 Conceptual

expert

How does NestJS handle missing query parameters with default values in method signatures?

Given this controller method:

  @Get('list')
  list(@Query('page') page: number = 1) {
    return page;
  }

If the client calls /list without any query parameters, what will be the returned value?

NestJS

  @Get('list')
  list(@Query('page') page: number = 1) {
    return page;
  }

A undefined

B 1

C null

D NaN

💡 Hint

Consider how NestJS injects query parameters and how default values in TypeScript work with decorators.

The default value = 1 in the method signature does not apply because NestJS injects undefined when the query parameter is missing. The decorator parameter overrides the default, so page is undefined. To have a default, you must handle it inside the method or use pipes.