instanceof type guards in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the object is an instance of the class Dog.

Typescript

if (pet [1] Dog) {
  console.log("It's a dog!");
}

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

Aequals

Btypeof

Cin

Dinstanceof

Attempts:

3 left

💡 Hint

Common Mistakes

Using typeof instead of instanceof

Using in operator which checks properties, not types

The instanceof operator checks if an object is an instance of a class or constructor function.

2fill in blank

medium

Complete the function to return true if the pet is a Cat using instanceof.

Typescript

function isCat(pet: any): pet is Cat {
  return pet [1] Cat;
}

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

Ain

Binstanceof

Ctypeof

Dequals

Attempts:

3 left

💡 Hint

Common Mistakes

Using typeof which returns 'object' for objects

Using in which checks for properties, not types

The instanceof operator is used here to check if pet is an instance of Cat.

3fill in blank

hard

Fix the error in the code to correctly check if vehicle is an instance of Truck.

Typescript

if (vehicle [1] Truck) {
  vehicle.loadCargo();
}

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

Ainstanceof

Btypeof

C===

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == or === instead of instanceof

Using typeof which returns 'object' for objects

Only instanceof correctly checks if vehicle is an instance of Truck. Using == or === compares references, not types.

4fill in blank

hard

Fill both blanks to create a type guard that checks if pet is a Bird and calls fly().

Typescript

if (pet [1] Bird) {
  pet.[2]();
}

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

Ainstanceof

Brun

Cfly

Dwalk

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong operator like typeof

Calling a method not defined on Bird like walk or run

The instanceof operator checks the type, and fly() is the method called on Bird instances.

5fill in blank

hard

Fill all three blanks to create a type guard that checks if shape is a Circle and returns its radius.

Typescript

function getRadius(shape: Shape): number | null {
  if (shape [1] Circle) {
    return shape.[2];
  } else {
    return [3];
  }
}

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

Ainstanceof

Bradius

Cnull

Ddiameter

Attempts:

3 left

💡 Hint

Common Mistakes

Returning diameter instead of radius

Using typeof instead of instanceof

Returning 0 instead of null when not a Circle

instanceof checks if shape is a Circle, then returns its radius. Otherwise, it returns null.