Bridge Design Pattern Explained

The Bridge pattern separates an abstraction from its implementation so each can vary independently, avoiding a class explosion from combining two dimensions of variation.

The concept

Without it, shapes × colours would need RedCircle, BlueCircle, RedSquare... With Bridge, Shape holds a Color object and both hierarchies grow separately.

The abstraction delegates the platform-specific work to an implementor interface.

Two hierarchies joined by composition

Practical examples

Sender implementors

class EmailSender { send(m) { /* smtp */ } }
class SmsSender   { send(m) { /* gateway */ } }

Abstractions use them

class Alert { constructor(sender) { this.sender = sender } fire(t) { this.sender.send('ALERT: ' + t) } }
class Reminder { constructor(sender) { this.sender = sender } fire(t) { this.sender.send('Reminder: ' + t) } }
new Alert(new SmsSender()).fire('disk full')

Combinations without new classes

2 abstractions × 2 senders = 4 behaviours, 4 small classes

Common mistakes

• Using Bridge when only one dimension varies.
• Confusing it with Adapter.
• Over-engineering early.

Key takeaways

• Split abstraction and implementation.
• Avoids class explosion.
• Uses composition.

FAQ

Bridge vs Adapter?

Bridge is designed up front to decouple; Adapter fixes incompatibility after the fact.

Bridge vs Strategy?

Structurally similar; Bridge targets structure, Strategy targets algorithms.