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Documentation Index

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Architecture

The Mini POS System uses IndexedDB for client-side data persistence. The database provides a simple, promise-based API for managing products and sales records.

​
Database Configuration

const DB_NAME = 'pos-db';
const DB_VER = 1;

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Schema

The database contains two object stores:

​
Products Store

  • Name: products
  • Key Path: id (auto-increment)
  • Indexes: None
  • Structure: 
    {
  id: number,        // Auto-generated
  name: string,      // Product name
  price: number      // Product price
}

​
Sales Store

  • Name: sales
  • Key Path: id (auto-increment)
  • Indexes: date (for range queries)
  • Structure: 
    {
  id: number,        // Auto-generated
  date: string,      // ISO 8601 date string
  items: Array,      // Array of sale items
  total: number      // Total sale amount
}

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Core Functions

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openDB()

Opens a connection to the IndexedDB database. Creates object stores if they don’t exist.
​
Promise<IDBDatabase>
Promise
Resolves with the database connection
Implementation:
js/db.js
function openDB() {
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, DB_VER);
    req.onupgradeneeded = () => {
      const db = req.result;
      if (!db.objectStoreNames.contains('products')) {
        db.createObjectStore('products', { keyPath: 'id', autoIncrement: true });
      }
      if (!db.objectStoreNames.contains('sales')) {
        const store = db.createObjectStore('sales', { keyPath: 'id', autoIncrement: true });
        store.createIndex('date', 'date');
      }
    };
    req.onsuccess = () => resolve(req.result);
    req.onerror = () => reject(req.error);
  });
}
Error Handling:
  • Rejects if the database cannot be opened
  • Rejects if there are permission issues
  • Rejects if IndexedDB is not supported

​
tx()

Helper function for executing transactions. Simplifies transaction management by handling connection and cleanup.
​
store
string
required
Name of the object store (‘products’ or ‘sales’)
​
mode
string
required
Transaction mode: ‘readonly’ or ‘readwrite’
​
fn
function
required
Callback function that receives the object store and performs operations
​
Promise<any>
Promise
Resolves with the result of the transaction
Implementation:
js/db.js
async function tx(store, mode, fn) {
  const db = await openDB();
  return new Promise((resolve, reject) => {
    const t = db.transaction(store, mode);
    const s = t.objectStore(store);
    const out = fn(s);
    t.oncomplete = () => resolve(out?.result ?? out);
    t.onerror = () => reject(t.error);
  });
}
Error Handling:
  • Rejects if the database connection fails
  • Rejects if the transaction fails
  • Rejects if the object store doesn’t exist

​
Connection Management

The database connection is managed automatically:
  1. openDB() is called for each transaction
  2. IndexedDB returns cached connections when available
  3. Connections are automatically closed after transactions complete
  4. Schema upgrades happen automatically on version changes

​
Usage Pattern

All database operations follow this pattern: 
// 1. Import the function
import { getProducts } from './js/db.js';

// 2. Call the async function
const products = await getProducts();

// 3. Handle errors with try/catch
try {
  const products = await getProducts();
  console.log(products);
} catch (error) {
  console.error('Database error:', error);
}

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