feat: add examples

examples/01-SRP/srp-bad.ts

@@ -0,0 +1,19 @@
+/* tslint:disable:max-classes-per-file */
+
+// Bad SRP
+
+class UserSettings {
+  constructor(user) {
+    this.user = user;
+  }
+
+  public changeSettings(settings) {
+    if (this.verifyCredentials()) {
+      // ...
+    }
+  }
+
+  public verifyCredentials() {
+    // ...
+  }
+}

examples/01-SRP/srp-good.ts

@@ -0,0 +1,26 @@
+/* tslint:disable:max-classes-per-file */
+
+// Good SRP
+
+class UserAuth {
+  constructor(user) {
+    this.user = user;
+  }
+
+  public verifyCredentials() {
+    // ...
+  }
+}
+
+class UserSettings {
+  constructor(user) {
+    this.user = user;
+    this.auth = new UserAuth(user);
+  }
+
+  public changeSettings(settings) {
+    if (this.auth.verifyCredentials()) {
+      // ...
+    }
+  }
+}

examples/02-OCP/ocp-bad.ts

@@ -0,0 +1,43 @@
+/* tslint:disable:max-classes-per-file */
+
+// Bad OCP
+
+class AjaxAdapter extends Adapter {
+  constructor() {
+    super();
+    this.name = "ajaxAdapter";
+  }
+}
+
+class NodeAdapter extends Adapter {
+  constructor() {
+    super();
+    this.name = "nodeAdapter";
+  }
+}
+
+class HttpRequester {
+  constructor(adapter) {
+    this.adapter = adapter;
+  }
+
+  public fetch(url) {
+    if (this.adapter.name === "ajaxAdapter") {
+      return makeAjaxCall(url).then((response) => {
+        // transform response and return
+      });
+    } else if (this.adapter.name === "httpNodeAdapter") {
+      return makeHttpCall(url).then((response) => {
+        // transform response and return
+      });
+    }
+  }
+}
+
+function makeAjaxCall(url) {
+  // request and return promise
+}
+
+function makeHttpCall(url) {
+  // request and return promise
+}

examples/02-OCP/ocp-good.ts

@@ -0,0 +1,38 @@
+/* tslint:disable:max-classes-per-file */
+
+// Good OCP
+
+class AjaxAdapter extends Adapter {
+  constructor() {
+    super();
+    this.name = "ajaxAdapter";
+  }
+
+  public request(url) {
+    // request and return promise
+  }
+}
+
+class NodeAdapter extends Adapter {
+  constructor() {
+    super();
+    this.name = "nodeAdapter";
+  }
+
+  public request(url) {
+    // request and return promise
+  }
+}
+
+class HttpRequester {
+  constructor(adapter) {
+    this.adapter = adapter;
+  }
+
+  public fetch(url) {
+    return this.adapter.request(url)
+      .then((response) => {
+        // transform response and return
+      });
+  }
+}

examples/03-LSP/lsp-bad.ts

@@ -0,0 +1,54 @@
+/* tslint:disable:max-classes-per-file */
+
+// Bad LSP
+
+class Rectangle {
+  constructor() {
+    this.width = 0;
+    this.height = 0;
+  }
+
+  public setColor(color) {
+    // ...
+  }
+
+  public render(area) {
+    // ...
+  }
+
+  public setWidth(width) {
+    this.width = width;
+  }
+
+  public setHeight(height) {
+    this.height = height;
+  }
+
+  public getArea() {
+    return this.width * this.height;
+  }
+}
+
+class Square extends Rectangle {
+  public setWidth(width) {
+    this.width = width;
+    this.height = width;
+  }
+
+  public setHeight(height) {
+    this.width = height;
+    this.height = height;
+  }
+}
+
+function renderLargeRectangles(rectangles) {
+  rectangles.forEach((rectangle) => {
+    rectangle.setWidth(4);
+    rectangle.setHeight(5);
+    const area = rectangle.getArea(); // BAD: Returns 25 for Square. Should be 20.
+    rectangle.render(area);
+  });
+}
+
+const rectangles = [new Rectangle(), new Rectangle(), new Square()];
+renderLargeRectangles(rectangles);

examples/03-LSP/lsp-good.ts

@@ -0,0 +1,46 @@
+/* tslint:disable:max-classes-per-file */
+
+// Good LSP
+
+class Shape {
+  public setColor(color) {
+    // ...
+  }
+
+  public render(area) {
+    // ...
+  }
+}
+
+class Rectangle extends Shape {
+  constructor(width, height) {
+    super();
+    this.width = width;
+    this.height = height;
+  }
+
+  public getArea() {
+    return this.width * this.height;
+  }
+}
+
+class Square extends Shape {
+  constructor(length) {
+    super();
+    this.length = length;
+  }
+
+  public getArea() {
+    return this.length * this.length;
+  }
+}
+
+function renderLargeShapes(shapes) {
+  shapes.forEach((shape) => {
+    const area = shape.getArea();
+    shape.render(area);
+  });
+}
+
+const shapes = [new Rectangle(4, 5), new Rectangle(4, 5), new Square(5)];
+renderLargeShapes(shapes);

examples/04-ISP/isp-bad.ts

@@ -0,0 +1,25 @@
+// Bad ISP
+
+class DOMTraverser {
+  constructor(settings) {
+    this.settings = settings;
+    this.setup();
+  }
+
+  public setup() {
+    this.rootNode = this.settings.rootNode;
+    this.animationModule.setup();
+  }
+
+  public traverse() {
+    // ...
+  }
+}
+
+const $ = new DOMTraverser({
+  rootNode: document.getElementsByTagName("body"),
+  animationModule() {
+    // Most of the time, we won't need to animate when traversing.
+  },
+  // ...
+});

examples/04-ISP/isp-good.ts

@@ -0,0 +1,33 @@
+// Good ISP
+
+class DOMTraverser {
+  constructor(settings) {
+    this.settings = settings;
+    this.options = settings.options;
+    this.setup();
+  }
+
+  public setup() {
+    this.rootNode = this.settings.rootNode;
+    this.setupOptions();
+  }
+
+  public setupOptions() {
+    if (this.options.animationModule) {
+      // ...
+    }
+  }
+
+  public traverse() {
+    // ...
+  }
+}
+
+const $ = new DOMTraverser({
+  options: {
+    animationModule() {
+      // ...
+    },
+  },
+  rootNode: document.getElementsByTagName("body"),
+});

examples/05-DIP/dip-bad.ts

@@ -0,0 +1,32 @@
+/* tslint:disable:max-classes-per-file */
+
+// Bad DIP
+
+class InventoryRequester {
+  constructor() {
+    this.REQ_METHODS = ["HTTP"];
+  }
+
+  public requestItem(item) {
+    // ...
+  }
+}
+
+class InventoryTracker {
+  constructor(items) {
+    this.items = items;
+
+    // BAD: We have created a dependency on a specific request implementation.
+    // We should just have requestItems depend on a request method: `request`
+    this.requester = new InventoryRequester();
+  }
+
+  public requestItems() {
+    this.items.forEach((item) => {
+      this.requester.requestItem(item);
+    });
+  }
+}
+
+const inventoryTracker = new InventoryTracker(["apples", "bananas"]);
+inventoryTracker.requestItems();

examples/05-DIP/dip-good.ts

@@ -0,0 +1,41 @@
+/* tslint:disable:max-classes-per-file */
+
+// Good DIP
+
+class InventoryTracker {
+  constructor(items, requester) {
+    this.items = items;
+    this.requester = requester;
+  }
+
+  public requestItems() {
+    this.items.forEach((item) => {
+      this.requester.requestItem(item);
+    });
+  }
+}
+
+class InventoryRequesterV1 {
+  constructor() {
+    this.REQ_METHODS = ["HTTP"];
+  }
+
+  public requestItem(item) {
+    // ...
+  }
+}
+
+class InventoryRequesterV2 {
+  constructor() {
+    this.REQ_METHODS = ["WS"];
+  }
+
+  public requestItem(item) {
+    // ...
+  }
+}
+
+// By constructing our dependencies externally and injecting them, we can easily
+// substitute our request module for a fancy new one that uses WebSockets.
+const inventoryTracker = new InventoryTracker(["apples", "bananas"], new InventoryRequesterV2());
+inventoryTracker.requestItems();