Why prototypes are needed in Javascript - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a prototype method that returns a greeting.

Javascript

function Person(name) {
  this.name = name;
}
Person.prototype.greet = function() {
  return [1] + this.name;
};

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

A'Hello, '

Bthis.name + 'Hello'

C'Hi ' + this.age

D'Goodbye, '

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong property like this.age instead of this.name

Putting the name before the greeting

The prototype method should return a greeting string followed by the person's name. Using 'Hello, ' + this.name achieves this.

2fill in blank

medium

Complete the code to add a shared property to all objects created by the constructor.

Javascript

function Car(model) {
  this.model = model;
}
Car.prototype.wheels = [1];

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

A0

B2

C4

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Setting wheels to 2 or 0 which is incorrect for cars

Leaving wheels undefined

Most cars have 4 wheels, so setting wheels to 4 on the prototype shares this property with all car objects.

3fill in blank

hard

Fix the error in the prototype method to correctly calculate age.

Javascript

function Person(birthYear) {
  this.birthYear = birthYear;
}
Person.prototype.getAge = function(currentYear) {
  return currentYear [1] this.birthYear;
};

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

A+

B*

C/

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or multiplication which gives wrong results

Using division which is incorrect here

To calculate age, subtract the birth year from the current year.

4fill in blank

hard

Fill both blanks to create a prototype method that checks if a number is even.

Javascript

function NumberCheck(num) {
  this.num = num;
}
NumberCheck.prototype.isEven = function() {
  return this.num [1] 2 [2] 0;
};

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

A%

B===

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of ===

Using == which is less strict than ===

The modulo operator (%) finds the remainder. If this.num % 2 === 0, the number is even.

5fill in blank

hard

Fill all three blanks to create a prototype method that returns a formatted description.

Javascript

function Book(title, author) {
  this.title = title;
  this.author = author;
}
Book.prototype.getDescription = function() {
  return [1] + ': ' + [2] + ' by ' + [3];
};

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

Athis.title

Bthis.author

Ctitle

Dauthor

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names without this

Mixing up title and author

The method should return the book's title followed by the author. Using this.title and this.author accesses the object's properties.