Add Observer Pattern and his script

Author: Joao Paulo Monteiro

observer/Follower.js

@@ -0,0 +1,6 @@
+class Follower{
+ update(data){
+ console.log(`Awwnnn... You're ${data} <3`);
+ }
+}
+export default Follower;

observer/Hater.js

@@ -0,0 +1,6 @@
+class Hater{
+ update(data){
+ console.log(`Argh! Bad thing. You're ${data}? Shame!`);
+ }
+}
+export default Hater;

observer/Observable.js

@@ -0,0 +1,20 @@
+class Observable{
+
+ constructor(){
+ this._listeners = [];
+ }
+
+ subscribe(subscriber){
+ this._listeners.push(subscriber);
+ }
+
+ unsubscribe(unsubscriber){
+ this._listeners = this._listeners.filter((listener) => listener !== unsubscriber);
+ }
+
+ notify(data){
+ this._listeners.forEach(listener => listener.update(data));
+ }
+}
+
+export default Observable;

observer/Stalker.js

@@ -0,0 +1,6 @@
+class Stalker{
+ update(data){
+ console.log(`Hmm... I'm looking you ${data}...`);
+ }
+}
+export default Stalker;

observer/User.js

@@ -0,0 +1,13 @@
+import Observable from './Observable';
+class User extends Observable{
+
+ constructor(){
+ super();
+ }
+
+ doSomething(data){
+ console.log(`I'm ${data}`);
+ this.notify(data);
+ }
+}
+export default User;

observer/main.js

@@ -0,0 +1,26 @@
+import User from './User';
+import Follower from './Follower';
+import Stalker from './Stalker';
+import Hater from './Hater';
+
+console.log('Creating a user and some other profiles');
+const user = new User();
+const fan = new Follower();
+const stalker = new Stalker();
+const hater = new Hater();
+
+console.log('Some people starts to following our star!');
+user.subscribe(fan);
+user.subscribe(stalker);
+user.subscribe(hater);
+
+console.log('Our star starts to act! Let\'s see what happens...');
+
+user.doSomething('walking on the street');
+user.doSomething('running on the street');
+user.doSomething('smiling to everyone!');
+
+console.log('Our start finally managed to mislead the hater');
+user.unsubscribe(hater);
+
+user.doSomething('Acting normally with no worries');

package.json

@@ -4,7 +4,8 @@
  "sucrase": "^3.10.1"
  },
  "scripts": {
- "strategy": "nodemon strategy/main.js"
+ "strategy": "nodemon strategy/main.js",
+ "observer": "nodemon observer/main.js"
  },
  "name": "design_patterns",
  "version": "1.0.0",