Prototype inheritance in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is prototype inheritance in JavaScript?

Prototype inheritance is a way objects in JavaScript can share properties and methods through a linked prototype object. When you access a property, JavaScript looks for it on the object, and if not found, it checks the prototype chain.

beginner

How do you set the prototype of an object in JavaScript?

You can set the prototype of an object using Object.create(proto) to create a new object with proto as its prototype, or by using Object.setPrototypeOf(obj, proto).

intermediate

What is the role of constructor in prototype inheritance?

The constructor property points back to the function that created the object. It helps identify the type of the object and is useful when creating new instances.

beginner

Explain the prototype chain in simple terms.

The prototype chain is like a family tree for objects. If an object doesn’t have a property, JavaScript looks up to its prototype, then that prototype’s prototype, and so on, until it finds the property or reaches the end.

beginner

How does JavaScript find a method when you call it on an object?

JavaScript first looks for the method on the object itself. If it’s not there, it looks up the prototype chain until it finds the method or reaches the end (null).

Which of the following is true about prototype inheritance in JavaScript?

A Objects inherit properties directly from other objects via the prototype chain.

B JavaScript uses class-based inheritance only.

C Prototype inheritance copies properties from one object to another.

D Prototype inheritance is not supported in JavaScript.

JavaScript uses prototype-based inheritance where objects inherit properties through a linked prototype chain.

How can you create a new object that inherits from another object parentObj?

A var child = Object.assign({}, parentObj);

B var child = new Object(parentObj);

C var child = parentObj();

D var child = Object.create(parentObj);

Object.create(parentObj) creates a new object with parentObj as its prototype.

What does the constructor property of an object refer to?

A The object's parent in the prototype chain.

B The function that created the object.

C The prototype object.

D The object's own properties.

The constructor property points to the function that created the object.

If a property is not found on an object, where does JavaScript look next?

A In the object's constructor.

B In the global variables.

C In the object's prototype.

D It throws an error immediately.

JavaScript looks up the prototype chain to find the property.

What will Object.getPrototypeOf(obj) return?

A The prototype object of <code>obj</code>.

B The constructor function of <code>obj</code>.

C The properties of <code>obj</code>.

D The global object.

Object.getPrototypeOf(obj) returns the prototype linked to obj.

Describe how prototype inheritance works in JavaScript and why it is useful.

Think about how objects share features without copying.

Explain how to create an object that inherits from another object and how to access inherited properties.

Consider how JavaScript finds properties when you use dot notation.