Why patterns matter for safety in Typescript - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

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

Typescript

let userName: [1] = "Alice";

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

Astring

Bany

Cnumber

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'any' type which disables safety checks.

Using string ensures the variable only holds text, which is safer than any.

2fill in blank

medium

Complete the code to define a function parameter with a safe type.

Typescript

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

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

Anumber

Bboolean

Cstring

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'any' which can cause unexpected errors.

Defining the parameter as string ensures only text is accepted, preventing errors.

3fill in blank

hard

Fix the error by choosing the correct type for the variable.

Typescript

let age: [1] = "30";

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

Aboolean

Bnumber

Cany

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'number' type with a string value causes errors.

The value is a string, so the type must be string to avoid type errors.

4fill in blank

hard

Fill both blanks to create a safe object type and assign it.

Typescript

type User = { name: [1]; age: [2]; };
const user: User = { name: "Bob", age: 25 };

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

Astring

Bnumber

Cboolean

Dany

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing types or using 'any' reduces safety.

The name should be string and age should be number for type safety.

5fill in blank

hard

Fill all three blanks to safely check a variable's type before using it.

Typescript

function printAge(age: [1] | [2]) {
  if (typeof age === [3]) {
    console.log(`Age is ${age}`);
  } else {
    console.log("Invalid age");
  }
}

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

Anumber

Bstring

C"number"

D"string"

Attempts:

3 left

💡 Hint

Common Mistakes

Using type names instead of string literals in typeof check.

The function accepts number or string. The typeof check must compare to the string "string" to be correct.