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Facade

 This pattern provides a simplified interface to a complex subsystem, allowing clients to interact with the subsystem through a single, unified interface. This can be useful when you want to hide the complexity of a subsystem from clients, and provide a more convenient and easy-to-use interface for interacting with the subsystem.


Here is an example of the facade pattern in JavaScript:


class Subsystem1 {

 operation1() {

  console.log('Subsystem1 operation1.');

 }

 operation2() {

  console.log('Subsystem1 operation2.');

 }

}

class Subsystem2 {

 operation1() {

  console.log('Subsystem2 operation1.');

 }

 operation2() {

  console.log('Subsystem2 operation2.');

 }

}

class Facade {

 constructor(subsystem1, subsystem2) {

  this.subsystem1 = subsystem1;

  this.subsystem2 = subsystem2;

 }

 operation() {

  console.log('Facade operation.');

  this.subsystem1.operation1();

  this.subsystem1.operation2();

  this.subsystem2.operation1();

  this.subsystem2.operation2();

 }

}

const subsystem1 = new Subsystem1();

const subsystem2 = new Subsystem2();

const facade = new Facade(subsystem1, subsystem2);

facade.operation();

// Output:

// Facade operation.

// Subsystem1 operation1.

// Subsystem1 operation2.

// Subsystem2 operation1.

// Subsystem2 operation2.


In this example, the Subsystem1 and Subsystem2 classes represent complex subsystems that have multiple operations, and the Facade class provides a simplified interface for interacting with these subsystems. The Facade class has a constructor that takes instances of the Subsystem1 and Subsystem2 classes as arguments, and has an operation() method that performs a set of operations on the subsystems.

To use the facade pattern, we first create instances of the Subsystem1 and Subsystem2 classes, which represent the complex subsystems that we want to interact with. Then, we create an instance of the Facade class, passing the instances of the Subsystem1 and Subsystem2 classes as arguments to the constructor.

This creates a facade object that wraps the complex subsystems and provides a simplified interface for interacting with them. When we call the operation() method on the facade object, it performs a set of operations on the wrapped subsystems, hiding the complexity of the subsystems from the client.