[Applied] Build a Mini Inventory Management System

This lesson combines the interface, union types, enum, and classes you've learned so far to build a simple inventory management system — the capstone of this TypeScript introduction.

In a real business system, a common combination is defining a data shape like "product" as an interface, expressing a fixed set of options like "stock status" as an enum or literal type, and bundling them together into a class to operate on.

The example defines a product's shape with interface Item, manages stock status with enum Status, and bundles adding items and generating a report together in class Inventory.

The type annotations, interfaces, enums, and class inheritance covered across these lessons are foundational ideas in real business-system design too. Building the habit of writing even small programs while staying conscious of types is the shortcut to using TypeScript professionally.

📖 Reference code

enum Status {
  InStock,
  LowStock,
  OutOfStock,
}

interface Item {
  name: string;
  quantity: number;
}

class Inventory {
  private items: Item[] = [];

  add(item: Item): void {
    this.items.push(item);
  }

  statusOf(item: Item): Status {
    if (item.quantity === 0) return Status.OutOfStock;
    if (item.quantity < 5) return Status.LowStock;
    return Status.InStock;
  }

  report(): void {
    for (const item of this.items) {
      console.log(`${item.name}: ${item.quantity} (${Status[this.statusOf(item)]})`);
    }
  }
}

const inv = new Inventory();
inv.add({ name: "Notebook", quantity: 12 });
inv.add({ name: "Eraser", quantity: 3 });
inv.add({ name: "Ruler", quantity: 0 });
inv.report();

✍️ Your code

Type your code, then press "Run"

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