Template Method in TypeScript

/** * The Abstract Class defines a template method that contains a skeleton of some * algorithm, composed of calls to (usually) abstract primitive operations. * * Concrete subclasses should implement these operations, but leave the template * method itself intact. */ abstract class AbstractClass { /** * The template method defines the skeleton of an algorithm. */ public templateMethod(): void { this.baseOperation1(); this.requiredOperations1(); this.baseOperation2(); this.hook1(); this.requiredOperation2(); this.baseOperation3(); this.hook2(); } /** * These operations already have implementations. */ protected baseOperation1(): void { console.log('AbstractClass says: I am doing the bulk of the work'); } protected baseOperation2(): void { console.log('AbstractClass says: But I let subclasses override some operations'); } protected baseOperation3(): void { console.log('AbstractClass says: But I am doing the bulk of the work anyway'); } /** * These operations have to be implemented in subclasses. */ protected abstract requiredOperations1(): void; protected abstract requiredOperation2(): void; /** * These are "hooks." Subclasses may override them, but it's not mandatory * since the hooks already have default (but empty) implementation. Hooks * provide additional extension points in some crucial places of the * algorithm. */ protected hook1(): void { } protected hook2(): void { } } /** * Concrete classes have to implement all abstract operations of the base class. * They can also override some operations with a default implementation. */ class ConcreteClass1 extends AbstractClass { protected requiredOperations1(): void { console.log('ConcreteClass1 says: Implemented Operation1'); } protected requiredOperation2(): void { console.log('ConcreteClass1 says: Implemented Operation2'); } } /** * Usually, concrete classes override only a fraction of base class' operations. */ class ConcreteClass2 extends AbstractClass { protected requiredOperations1(): void { console.log('ConcreteClass2 says: Implemented Operation1'); } protected requiredOperation2(): void { console.log('ConcreteClass2 says: Implemented Operation2'); } protected hook1(): void { console.log('ConcreteClass2 says: Overridden Hook1'); } } /** * The client code calls the template method to execute the algorithm. Client * code does not have to know the concrete class of an object it works with, as * long as it works with objects through the interface of their base class. */ function clientCode(abstractClass: AbstractClass) { // ... abstractClass.templateMethod(); // ... } console.log('Same client code can work with different subclasses:'); clientCode(new ConcreteClass1()); console.log(''); console.log('Same client code can work with different subclasses:'); clientCode(new ConcreteClass2()); 

Same client code can work with different subclasses: AbstractClass says: I am doing the bulk of the work ConcreteClass1 says: Implemented Operation1 AbstractClass says: But I let subclasses override some operations ConcreteClass1 says: Implemented Operation2 AbstractClass says: But I am doing the bulk of the work anyway Same client code can work with different subclasses: AbstractClass says: I am doing the bulk of the work ConcreteClass2 says: Implemented Operation1 AbstractClass says: But I let subclasses override some operations ConcreteClass2 says: Overridden Hook1 ConcreteClass2 says: Implemented Operation2 AbstractClass says: But I am doing the bulk of the work anyway