Merge pull request #8 from shubhamgautam89/pattern/observer

mixin pattern

patterns/mixin/mixin.js

@@ -0,0 +1,45 @@
+/*
+    A mixin is an object that we can use in order to add reusable functionality to another object or class, without using inheritance. We can't use mixins on their own: their sole purpose is to add functionality to objects or classes without inheritance.
+*/
+
+//simple example with prototype
+
+export class Dog {
+  constructor(name) {
+    this.name = name;
+  }
+}
+
+export class Bird {
+  constructor(name) {
+    this.name = name;
+  }
+}
+
+export class Fish {
+  constructor(name) {
+    this.name = name;
+  }
+}
+
+const dogFunctionality = {
+  bark: () => "Woof!",
+  wagTail: () => "Wagging my tail",
+  play: () => "Playing!",
+};
+
+const flyMixin = {
+  fly() {
+    return "fly";
+  },
+};
+
+const swimMixin = {
+  swim() {
+    return "swim";
+  },
+};
+
+Object.assign(Dog.prototype, dogFunctionality);
+Object.assign(Bird.prototype, flyMixin);
+Object.assign(Fish.prototype, swimMixin);

patterns/mixin/mixin.test.js

@@ -0,0 +1,23 @@
+import { Bird, Dog, Fish } from "./mixin";
+
+const tommyDog = new Dog("tommy");
+const nemoFish = new Fish("nemo");
+const redBird = new Bird("red");
+
+test("dog test cases", () => {
+  expect(tommyDog.name).toBe("tommy");
+  expect(tommyDog.bark()).toBe("Woof!");
+  expect(tommyDog.wagTail()).toBe("Wagging my tail");
+});
+
+test("fish test cases", () => {
+  expect(nemoFish.name).toBe("nemo");
+  expect(nemoFish.swim()).toBe("swim");
+  expect(nemoFish).not.toHaveProperty("fly");
+});
+
+test("bird test cases", () => {
+  expect(redBird.name).toBe("red");
+  expect(redBird.fly()).toBe("fly");
+  expect(redBird).not.toHaveProperty("swim");
+});