Week 4

Over the past three weeks you've transformed data with array methods, managed async flows with callbacks and Promises, and fetched from a real API. But all your data has been plain objects - no validation, no built-in behavior, no structure beyond what you remember to add each time.

This week you'll learn classes: blueprints for creating objects with consistent structure and built-in behavior. You'll build Tea, Order, and Inventory classes that validate data, calculate totals, and work together - just like the models behind the Tea Shop API you've been using.

Contents

• Preparation

• Slides

• Session Plan (for mentors)

• Session Materials

• Assignment

Learning Goals

By the end of this session, you will be able to:

• Understand why classes exist (organizing data with behavior)

• Declare a class using class, constructor, and this

• Instantiate objects from classes using new

• Add methods to classes and call them on instances

• Use this to access and modify instance state

• Use static methods for utility operations on a class

• Use inheritance with extends and super()

• Understand the difference between a class (blueprint) and an object (instance)

After this session you will understand code like this

// From scattered plain objects...
const tea = { name: "Sencha", pricePerGram: 0.12, origin: "Japan" };
// No validation, no behavior, no consistency

// ...to structured classes with built-in behavior
class Tea {
  constructor(name, pricePerGram, origin) {
    this.name = name;
    this.pricePerGram = pricePerGram;
    this.origin = origin;
  }

  priceFor(grams) {
    return this.pricePerGram * grams;
  }
}

const sencha = new Tea("Sencha", 0.12, "Japan");
console.log(sencha.priceFor(100)); // 12