Why should you care?

Classes encapsulate behavior — an Account class can format balance; a service class wraps HTTP.

See it live — copy this example

Paste into your MeanVerse project (Angular + Express + MongoDB), then run with ng serve / node / mongosh as noted.

export class Money {
  constructor(public readonly cents: number, public readonly currency: string) {}

  add(other: Money): Money {
    if (this.currency !== other.currency) throw new Error('Currency mismatch');
    return new Money(this.cents + other.cents, this.currency);
  }

  format(): string {
    return new Intl.NumberFormat('en-US', { style: 'currency', currency: this.currency })
      .format(this.cents / 100);
  }
}

What happened?

• readonly prevents reassignment.
• add returns new Money — immutable pattern safe for concurrent updates.
• format hides Intl details from callers.

Practice next

1. Model Money or Account as a class with methods.
2. Use private fields for internal state.
3. Inject class-based service in Angular with @Injectable.
4. Implement subtract and equals on Money.
5. Add static fromDollars(d: number) factory method.

Remember

Classes bundle data and behavior. Use for domain logic like Money, DateRange. Angular DI works naturally with classes.

Ledger precision

MeanVerse stores amounts in cents as integers inside Money class.

Outcome: Floating-point bugs avoided in transfer calculations.