Inheritance

Basics

• When you want to implement inheritance, you attach properties and methods to the prototype

• Every JS function has a prototype property

  • The prototype property is empty by default

  • The prototype property is not enumerable

• Every JS object has a prototype attribute

  • Points to the object's parent

  • Set automatically when the object is created

• All JS objects inherit the following properties and methods from Object.prototype:

  • constructor

  • hasOwnProperty()

  • isPrototypeOf()

  • propertyIsEnumerable()

  • toLocaleString()

  • toString()

  • valueOf()

Constructors

• Functions used for initializing new objects

• Called using the new keyword

• All objects inherit a constructor property that points to the constructor of the object

• If an object is created with an object literal, it inherits from Object.prototype; if an object is created from a constructor, it inherits from the constructor

Prototypes

• Every object's prototype is either null or references another object

• The prototype property is internal and hidden, though there's a few ways to access it

  • You can use myObject.__proto__

    • This is a historical getter/setter

    • Has been replaced with Object.getPrototypeOf and Object.setPrototypeOf

• Prototypes are only used for reading

  • All write/delete operations operate directly on the object

  • Accessor functions are an exception, since calling a setter is technically writing

• The this keyword is not affected by prototypes

• Currently, the recommended way of setting the prototype of an object is Object.create

Links

• JavaScript is Sexy - Javascript Prototype in Plain Language
• JavaScript.info - Prototypical Inheritance
• The Odin Project - Objects and Object Constructors