Prototype inheritance in Javascript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an object that inherits from another object using __proto__.

Javascript

const parent = { greet() { return 'Hello'; } };
const child = { __proto__: [1] };
console.log(child.greet());

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

Aparent

Bchild

CObject

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Setting __proto__ to the child itself causes no inheritance.

Using an empty object {} as prototype does not inherit parent's methods.

The __proto__ property sets the prototype of the object. Setting it to parent makes child inherit from parent.

2fill in blank

medium

Complete the code to check if child inherits the greet method from parent.

Javascript

const parent = { greet() { return 'Hi'; } };
const child = { __proto__: parent };
console.log('[1]' in child);

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

A'parent'

B'child'

C'greet'

D'hello'

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names instead of property names as strings.

Checking for 'parent' or 'child' which are not property names.

The in operator checks if a property exists in the object or its prototype chain. Here, 'greet' is the method inherited by child.

3fill in blank

hard

Fix the error in the code to properly set the prototype of child to parent using Object.setPrototypeOf.

Javascript

const parent = { speak() { return 'Hey'; } };
const child = {};
Object.setPrototypeOf(child, [1]);
console.log(child.speak());

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

Aparent

Bchild

C{}

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Passing child as the prototype causes no inheritance.

Passing an empty object {} does not link to parent.

Object.setPrototypeOf sets the prototype of the first argument to the second. Here, child should inherit from parent.

4fill in blank

hard

Fill both blanks to create a prototype chain where child inherits from parent and parent inherits from grandparent.

Javascript

const grandparent = { say() { return 'Hello from grandparent'; } };
const parent = { __proto__: [1] };
const child = { __proto__: [2] };
console.log(child.say());

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

Agrandparent

Bchild

Cparent

D{}

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing the prototype assignments breaks the chain.

Using empty objects {} breaks inheritance.

Setting parent.__proto__ to grandparent and child.__proto__ to parent creates a chain where child inherits from parent, which inherits from grandparent.

5fill in blank

hard

Fill all three blanks to create a function constructor Person, add a method to its prototype, and create an instance that uses that method.

Javascript

function [1](name) {
  this.name = name;
}
[2].prototype.sayName = function() {
  return `My name is ${this.name}`;
};
const person = new [3]('Alice');
console.log(person.sayName());

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

APerson

DHuman

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for constructor and prototype causes errors.

Adding methods directly to the instance instead of prototype.

The function constructor is named Person. We add sayName to Person.prototype. Then we create an instance with new Person('Alice') which inherits the method.