Classes

• Classes are like blueprints for objects that we want created
• An instance of a class is like an object created from the class blueprint
• Each instance has a different state from the next instance

Defining a Class

• The name of the class
  • TitleCase
• Constructor function:
  • Used to initialize an object
  • Used to communicate required data to initialize an object
• Instance variables:
  • The state of the thing or created object
  • this.camelCaseName to get and set the value
• Instance methods:
  • how the world interacts with the thing or created object
  • camelCase
  • Types of instance methods:
    • Accessors: get some data from the object
    • Mutators: changes the state of the data

ES6 Class Syntax

ES6 Class

Inheritance

We can make a child class of another class, parent class, by using the extend keyword

class Cat extends Animal {

}

ES5 Class Syntax

ES5 Class

Importing and Exporting Modules

Importing and Exporting Demo

Importing built-in Node modules or npm-installed modules

• can just specifiy in the require function the string of the module name

const mocha = require('mocha');

Exporting modules from your own code

• set module.exports to whatever you want to export from the file
• OR use exports dot notation to export a specific key in an object from a file

class Person {
  // ...
}
const hello = 'hello';
module.exports = {
  Person,
  hello
};

is the same as:

exports.Person = class Person {
  // ...
};
exports.hello = 'hello';

Importing modules from your own code

• need to specify the relative path in a string passed into the require function (don’t need to append the .js file extension)

const tax = require('../util/tax'); // will look into the util folder for tax.js

• can destructure objects when importing if you are importing an object:

in the file ../util/people.js:

class Person {
  // ...
}
const hello = 'hello';
module.exports = {
  Person,
  hello
};

can import Person into ./index.js by:

const { Person } = require('../util/people.js');

JavaScript Classes Learning Objectives

1. Define a constructor function using ES5 syntax.
2. Define a method on the prototype of a constructor function using ES5 syntax.
3. Declare a class using ES6 (ES2015) syntax.
4. Define an instance method on a class (ES6).
5. Define a static method on a class (ES6).
6. Instantiate an instance of a class using the new keyword.
7. Implement inheritance using the ES6 extends syntax for an ES6 class.
8. Utilize the super keyword in a child class to inherit from a parent class.
9. Utilize module.exports and require to import and export functions and class from one file to another.