Facade (Structural)

Intent / problem it solves

Provide a unified higher-level interface to a set of interfaces in a subsystem, simplifying common workflows and reducing coupling for most clients.

When to use / when NOT

Use when a module exposes many small services; wrap frequent sequences (checkout, deploy, onboarding).

Avoid when it becomes a god object; keep facades thin and push logic down.

Structure

Facade coordinates subsystem classes; clients depend only on the facade for common paths.

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Go example

package main

import "fmt"

type Inventory struct{}

func (Inventory) Reserve(sku string) bool { return sku != "" }

type Payment struct{}

func (Payment) Charge(amount int) bool { return amount > 0 }

type Shipping struct{}

func (Shipping) Schedule(address string) string { return "tracking-" + address }

type Storefront struct{}

func (Storefront) Buy(sku string, amount int, address string) (string, bool) {
	if !Inventory{}.Reserve(sku) || !Payment{}.Charge(amount) {
		return "", false
	}
	return Shipping{}.Schedule(address), true
}

func main() {
	tracking, ok := Storefront{}.Buy("book", 20, "Main St")
	fmt.Println(tracking, ok)
}

JavaScript example

class AuthService {
  signIn(credentials) {
    return { token: `tok-${credentials.user}` };
  }
}

class ProfileService {
  loadProfile(token) {
    return { token, name: 'Ada' };
  }
}

class SessionFacade {
  constructor(auth, profiles) {
    this.auth = auth;
    this.profiles = profiles;
  }

  openSession(credentials) {
    const session = this.auth.signIn(credentials);
    const profile = this.profiles.loadProfile(session.token);
    return { session, profile };
  }
}

const facade = new SessionFacade(new AuthService(), new ProfileService());
console.log(facade.openSession({ user: 'ada' }));

Interview phrase

“Facade is my narrow entry point: it sequences inventory, payment, and shipping so the mobile app calls one method instead of three services.”

Reference in LLD when a use case orchestrates multiple subsystems in LLD case studies.

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