Prototype pattern

Author: blue32a

README.md

@@ -7,3 +7,4 @@
 - [Abstract Factory](./src/AbstractFactory/README.md)
 - [Builder](./src/Builder/README.md)
 - [Factory Method](./src/FactoryMethod/README.md)
+- [Prototype](./src/Prototype/README.md)

src/Prototype/README.md

@@ -0,0 +1,23 @@
+## Prototype
+
+https://refactoring.guru/ja/design-patterns/prototype
+
+```mermaid
+classDiagram
+  class Prototype {
+    <<Interface>>
+    clone()
+  }
+  class ConcretePrototypeA {
+    clone()
+  }
+  class ConcretePrototypeB {
+    clone()
+  }
+  class Client {
+  }
+
+  ConcretePrototypeA ..|> Prototype
+  ConcretePrototypeB ..|> Prototype
+  Client ..> Prototype
+```

src/Prototype/index.ts

@@ -0,0 +1,60 @@
+export {};
+
+class Prototype {
+  public primitive: any;
+  public component: object;
+  public circularReference: ComponentWithBackReference;
+
+  public clone(): this {
+    const clone = Object.create(this);
+
+    clone.component = Object.create(this.component);
+
+    clone.circularReference = {
+      ...this.circularReference,
+      prototype: { ...this },
+    };
+
+    return clone;
+  }
+}
+
+class ComponentWithBackReference {
+  public prototype;
+
+  constructor(prototype: Prototype) {
+    this.prototype = prototype;
+  }
+}
+
+function clientCode() {
+  const p1 = new Prototype();
+  p1.primitive = 245;
+  p1.component = new Date();
+  p1.circularReference = new ComponentWithBackReference(p1);
+
+  const p2 = p1.clone();
+  if (p1.primitive === p2.primitive) {
+    console.log('Primitive field values have been carried over to a clone. Yay!');
+  } else {
+    console.log('Primitive field values have not been copied. Booo!');
+  }
+  if (p1.component === p2.component) {
+    console.log('Simple componet has not been cloned. Booo!');
+  } else {
+    console.log('Simple component has been cloned. Yay!');
+  }
+
+  if (p1.circularReference === p2.circularReference) {
+    console.log('Component with back reference has not been cloned. Booo!');
+  } else {
+    console.log('Component with back refarence has been cloned. Yay!');
+  }
+  if (p1.circularReference.prototype === p2.circularReference.prototype) {
+    console.log('Component with back reference is linked to original object. Booo!');
+  } else {
+    console.log('Component with back reference is linked to the clone. Yay!');
+  }
+}
+
+clientCode();

tsconfig.json

@@ -87,7 +87,7 @@
     // "strictNullChecks": true,                         /* When type checking, take into account 'null' and 'undefined'. */
     // "strictFunctionTypes": true,                      /* When assigning functions, check to ensure parameters and the return values are subtype-compatible. */
     // "strictBindCallApply": true,                      /* Check that the arguments for 'bind', 'call', and 'apply' methods match the original function. */
-    // "strictPropertyInitialization": true,             /* Check for class properties that are declared but not set in the constructor. */
+    "strictPropertyInitialization": false,             /* Check for class properties that are declared but not set in the constructor. */
     // "noImplicitThis": true,                           /* Enable error reporting when 'this' is given the type 'any'. */
     // "useUnknownInCatchVariables": true,               /* Default catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Ensure 'use strict' is always emitted. */