Class: extends

Classes can inherit from another using extends

the default super class is Object

a class A is an instance of Object

let A assert.equal(new A() instanceof Object, true);

when B extends A, B is also instance of Object

class A {} class B {} assert.equal(new B() instanceof A, true); assert.equal(new B() instanceof Object, true);

a class can extend null, and is not an instance of Object

class NullClass extends null { // This is how a class, that extends `null` can be written. constructor() { return Object.create(new.target.prototype); } } let nullInstance = new NullClass(); assert.equal(nullInstance instanceof Object, false);

instance of

when B inherits from A, new B() is also an instance of A

let A; class B extends A {} assert.equal(new B() instanceof A, true);

extend over multiple levels

class A {} class C extends B {} assert.equal(new C instanceof A, true);

Related Katas

Class

• creation
• accessors
• static
• extends
• more extends
• super in method
• super in constructor

Difficulty Level

BEGINNER

First Published

17 April 2015

Stats

5 tests to solve