Published May 08, 2022
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Have you ever used an access card to go through a door? There are multiple options to open that door i.e. it can be opened either using access card or by pressing a button that bypasses the security. The door’s main functionality is to open but there is a proxy added on top of it to add some functionality. Let me better explain it using the code example below.
Using the proxy pattern, a class represents the functionality of another class.
A proxy, in its most general form, is a class functioning as an interface to something else. A proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes. Use of the proxy can simply be forwarding to the real object, or can provide additional logic. In the proxy extra functionality can be provided, for example caching when operations on the real object are resource intensive, or checking preconditions before operations on the real object are invoked.
Taking our security door example from above. Firstly we have the door interface and an implementation of door
interface Door {
open();
close();
}
class LabDoor implements Door {
open(){
console.log("Opening lab door")
}
close() {
console.log("Closing the lab door")
}
}
Then we have a proxy to secure any doors that we want
class SecuredDoor {
protected door;
constructor(door) {
this.door = door
}
authenticate(password) {
return password === '$ecr@t'
}
open(password){
if (this.authenticate(password)) {
this.door.open()
} else {
console.log("Big no! It ain't possible")
}
}
close() {
this.door.close()
}
}
And here is how it can be used
const door = new SecuredDoor(new LabDoor())
door.open('invalid')
door.open('$ecr@t')
door.close()