Facade Pattern

Real world example

How do you turn on the computer? "Hit the power button" you say! That is what you believe because you are using a simple interface that computer provides on the outside, internally it has to do a lot of stuff to make it happen. This simple interface to the complex subsystem is a facade.

In plain words

Facade pattern provides a simplified interface to a complex subsystem.

Wikipedia says

A facade is an object that provides a simplified interface to a larger body of code, such as a class library.

Programmatic Example Taking our computer example from above. Here we have the computer class

class Computer {

    getElectricShock() {
        console.log('Ouch!')
    }

    makeSound() {
        console.log('Beep beep!')
    }

    showLoadingScreen() {
        console.log('Loading..')
    }

    bam() {
        console.log('Ready to be used!')
    }

    closeEverything() {
        console.log('Bup bup bup buzzzz!')
    }

    sooth() {
        console.log('Zzzzz')
    }

    pullCurrent() {
        console.log('Haaah!')
    }
}

Here we have the facade

class ComputerFacade
{
    constructor(computer) {
        this.computer = computer
    }

    turnOn() {
        this.computer.getElectricShock()
        this.computer.makeSound()
        this.computer.showLoadingScreen()
        this.computer.bam()
    }

    turnOff() {
        this.computer.closeEverything()
        this.computer.pullCurrent()
        this.computer.sooth()
    }
}

Now to use the facade

const computer = new ComputerFacade(new Computer())
computer.turnOn() // Ouch! Beep beep! Loading.. Ready to be used!
computer.turnOff() // Bup bup buzzz! Haah! Zzzzz