JavaScript OOP

Telerik Software Academy

• What is inheritance
• Inheritance in ES6
  • Super class calls

• Inheritance allows child classes to inherit the characteristics of an existing parent (base) class
  • Attributes (fields and properties)
  • Operations (methods)
• Child class can extend the parent class
  • Add new fields and methods
  • Redefine methods (modify existing behavior)

• Inheritance has a lot of benefits
  • Extensibility
  • Reusability (code reuse)
  • Provides abstraction
  • Eliminates redundant code
• Use inheritance for building is-a relationships
  • E.g. dog is-a animal (dogs are kind of animals)
• Don't use it to build has-a relationship
  • E.g. dog has-a name (dog is not kind of name)

• Inheritance implicitly gains all members from another class
  • All fields, methods, properties, events, …
  • Some members could be inaccessible (hidden)
• The class whose methods are inherited is called base (parent) class
• The class that gains new functionality is called derived (child) class

• ES6 introduces classes and a way to create classical OOP
  • Using the class keyword

class Mammal {
	constructor(age) {
		this._age = age;
	}
}

• Sub classing is done using the extend keyword

class Mammal {
	speak(str) {
		// mammals usually don't speak
	}
}

class Person extends Mammal {
	speak(str) {
		console.log(str);
	}
}

• super is used to refer to the parent class
  • super() calls the parent constructor
    • needed in order for this to refer to the correct object
  • super.method() calls .method() from the parent class

class Person extends Mammal {
  constructor(fname, lname, age) {
    super(age);
    this._fname = fname;
    this._lname = lname;
  }
  get fullname() {
    // getter property of fullname
  }
  set fullname(newfullname) {
    // setter property of fullname
  }
  // more class members…
}

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