Type annotation on variables in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Typescript

let age: [1] = 25;

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Anumber

Bstring

Cboolean

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using string type for a number variable.

Omitting the type annotation.

The variable age should be annotated with the number type to hold numeric values.

2fill in blank

medium

Complete the code to declare a constant isActive with type boolean.

Typescript

const isActive: [1] = true;

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

Astring

Bboolean

Cnumber

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Using string or number instead of boolean.

Forgetting to add the type annotation.

The variable isActive should be annotated with the boolean type to hold true or false values.

3fill in blank

hard

Fix the error in the code by adding the correct type annotation to names as an array of strings.

Typescript

let names: [1] = ["Alice", "Bob", "Charlie"];

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

Astring[]

Bstring

CArray<number>

Dnumber[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using string instead of string[].

Using number array types by mistake.

The variable names is an array of strings, so it should be annotated as string[].

4fill in blank

hard

Fill both blanks to declare a variable user as an object with name as string and age as number.

Typescript

let user: [1] = { name: "John", age: 30 }; // user has name: string and age: number

// Type annotation for user is [2]

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A{ name: string; age: number }

B{ name: number; age: string }

C{ name: string; age: string }

D{ name: number; age: number }

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the types of name and age.

Using string type for age.

The variable user is an object with name as string and age as number, so the type annotation is { name: string; age: number }.

5fill in blank

hard

Fill all three blanks to declare a variable coordinates as a tuple with two numbers: x and y.

Typescript

let coordinates: [1] = [[2], [3]];

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

A[number, number]

B10

C20

D[string, string]

Attempts:

3 left

💡 Hint

Common Mistakes

Using array type instead of tuple.

Using strings instead of numbers.

The variable coordinates is a tuple of two numbers, so the type is [number, number] and the values are numbers like 10 and 20.