Declaration file syntax (.d.ts) in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable of type string in a declaration file.

Typescript

declare let message: [1];

Drag options to blanks, or click blank then click option'

Astring

Bnumber

Cboolean

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'number' or 'boolean' instead of 'string' for text variables.

The declare keyword is used to declare variables in a declaration file. Here, message is declared as a string.

2fill in blank

medium

Complete the code to declare a function that takes a number and returns a string.

Typescript

declare function formatNumber(value: [1]): string;

Drag options to blanks, or click blank then click option'

Astring

Bboolean

Cnumber

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'string' as the parameter type instead of 'number'.

The function formatNumber takes a parameter value of type number and returns a string.

3fill in blank

hard

Fix the error in the interface declaration by completing the property type.

Typescript

interface User {
  id: [1];
  name: string;
}

Drag options to blanks, or click blank then click option'

Aboolean

Bnumber

Cany

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'string' or 'boolean' for the id property.

The id property is usually a number to uniquely identify a user.

4fill in blank

hard

Fill both blanks to declare a module and export a constant string.

Typescript

declare module "myModule" {
  export const version: [1];
  export function getName(): [2];
}

Drag options to blanks, or click blank then click option'

Astring

Bnumber

Cboolean

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using different types for version and getName return type.

The constant version and the return type of getName are both string types.

5fill in blank

hard

Fill all three blanks to declare a namespace with an interface and a function.

Typescript

declare namespace Utils {
  interface Logger {
    log(message: [1]): void;
  }
  function createLogger(level: [2]): Logger;
  const defaultLevel: [3];
}

Drag options to blanks, or click blank then click option'

Astring

Bnumber

Cboolean

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using number for log message or logging level.

The log method takes a string message. The level parameter and defaultLevel constant are boolean to indicate if logging is enabled or not.