Why type annotations are needed in Typescript - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with a number type annotation.

Typescript

let age: [1] = 30;

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

Aany

Bstring

Cboolean

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'string' instead of 'number' causes type errors.

Omitting the type annotation can lead to implicit 'any' type.

The number type annotation tells TypeScript that age must hold a number value.

2fill in blank

medium

Complete the function parameter with the correct type annotation.

Typescript

function greet(name: [1]) { console.log(`Hello, ${name}!`); }

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

Anumber

Bobject

Cstring

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'number' or 'boolean' causes errors when passing text.

Not specifying a type can lead to unexpected behavior.

The parameter name should be a string because it represents text.

3fill in blank

hard

Fix the error by adding the correct return type annotation to the function.

Typescript

function add(a: number, b: number): [1] { return a + b; }

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

Anumber

Bboolean

Cstring

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' means no value is returned, causing errors here.

Using 'string' or 'boolean' does not match the actual return value.

The function returns the sum of two numbers, so the return type is number.

4fill in blank

hard

Fill both blanks to create a typed object with a name and age.

Typescript

const person: { name: [1]; age: [2] } = { name: 'Alice', age: 25 };

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

Astring

Bnumber

Cboolean

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up types causes type errors.

Using 'any' loses the benefit of type checking.

The name is text, so it uses string. The age is a number, so it uses number.

5fill in blank

hard

Fill all three blanks to type a function that returns a boolean indicating if a number is positive.

Typescript

function isPositive(num: [1]): [2] { return num [3] 0; }

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

Astring

Bboolean

C>

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong types for parameters or return values.

Using incorrect comparison operators.

The parameter num is a number. The function returns a boolean. The comparison operator is >.