Unknown type vs any type in Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with the unknown type.

Typescript

let value: [1];

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

Aunknown

Bany

Cvoid

Dnever

Attempts:

3 left

💡 Hint

Common Mistakes

Using any instead of unknown disables type safety.

Confusing void with unknown.

The unknown type is used when the type is not known yet, unlike any which disables type checking.

2fill in blank

medium

Complete the code to assign a value of type unknown to a variable.

Typescript

let data: unknown = [1];

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

Atrue

B'hello'

C42

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign a value that is not valid syntax.

Confusing unknown with any in assignment.

You can assign any value to a variable of type unknown. Here, 42 is a valid number.

3fill in blank

hard

Fix the error in the code by adding a type check before assignment.

Typescript

let value: string;
let input: unknown = 'test';
if (typeof input === [1]) {
  value = input;
}

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

A'number'

B'object'

C'boolean'

D'string'

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning unknown directly without type check.

Using wrong type string in the check.

Before assigning input of type unknown to value of type string, we check if input is a string.

4fill in blank

hard

Fill both blanks to safely assign an unknown value to a number variable.

Typescript

let num: number;
let val: unknown = 10;
if (typeof val === [1]) {
  num = val [2] 0;
}

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

A'number'

B+

C-

D'string'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong type string in the check.

Missing arithmetic operation causing type errors.

Check if val is a number, then assign it to num. The + 0 ensures num is a number type.

5fill in blank

hard

Fill all three blanks to convert an any type to a string safely.

Typescript

let input: any = 123;
let output: string;
if (typeof input === [1]) {
  output = input [2] '';
} else {
  output = String([3]);
}

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

A'string'

B+

Cinput

Dinput.toString()

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking type before assignment.

Using wrong conversion method.

Check if input is a string, then concatenate with empty string to keep it string. Otherwise, convert input to string using String(input).