Mixins and Composition in Typescript Part 3

Let's look out how to use higher order functions to achieve reusablity. In Part 1 we learned how to use Mixins to achieve code reusablity. In Part 2 we used composition to achieve reusablity. In Part 3 we will use higher order functions to achieve reusablity.

Higher order Functions

We define two interfaces

interface CanFly {
  fly(): void
}

interface CanSwim {
  swim(): void
}

Next we implement two higher order functions. In the previous parts we used interfaces instead

function fly() {
  console.log('I can fly!')
}

function swim() {
  console.log('I can swim!')
}

Now, we create a higher-order function that takes an object and a set of methods to be added to that object:

function withMethods<T extends object, M extends object>(base: T, methods: M): T & M {
  return Object.assign(base, methods)
}

Laslty we create a Duck class that will call fly and swim

class Duck {}

const duck = withMethods(new Duck(), { fly, swim })

duck.fly() // Output: I can fly!
duck.swim() // Output: I can swim!

Conclusion

Reusability is achievable with different approaches. Mixins, Composition or higher order functions are just a few possibilities.