Type assertions in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assert that the variable value is of type string.

Typescript

let value: any = "hello";
let strValue = value as [1];

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Aboolean

Bnumber

Cstring

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong type in the assertion.

Forgetting to use the as keyword.

The as keyword is used for type assertions in TypeScript. Here, value as string tells the compiler to treat value as a string.

2fill in blank

medium

Complete the code to assert that the variable input is of type number.

Typescript

let input: any = 42;
let numInput = [1] as number;

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Adata

Binput

Cvalue

DnumInput

Attempts:

3 left

💡 Hint

Common Mistakes

Asserting the wrong variable.

Placing as before the variable.

You assert the type of the variable you want to convert. Here, input as number asserts that input is a number.

3fill in blank

hard

Fix the error in the code by completing the type assertion correctly.

Typescript

let data: any = "123";
let length = (data as [1]).length;

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Astring

Bnumber

Cboolean

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Asserting data as number and trying to access length.

Not using type assertion at all.

To access the length property, data must be asserted as a string.

4fill in blank

hard

Fill both blanks to assert the variable item as a string and then get its length.

Typescript

let item: any = "typescript";
let len = ([1] as [2]).length;

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Aitem

Bnumber

Cstring

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the variable and type in the assertion.

Using the wrong type in the assertion.

First, you assert item as a string using as string. Then you can access the length property.

5fill in blank

hard

Fill all three blanks to create a type assertion that converts input to a string and then gets the uppercase version.

Typescript

let input: any = "hello";
let upper = ([1] as [2]).[3]();

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Ainput

Bstring

CtoUpperCase

DtoLowerCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using toLowerCase instead of toUpperCase.

Asserting the wrong variable or type.

You assert input as a string and then call the toUpperCase() method to get the uppercase string.