Chaining and fluent interfaces

When you work with objects or arrays, there is another way of linking the execution of several calls together: by applying chaining. For example, when you work with arrays, if you apply a map() or filter() method, the result is a new array, to which you can then apply another map() or filter() function, and so forth. We used these methods when we defined the range() function back in the Working with ranges section of Chapter 5, Programming Declaratively:

const range = (start: number, stop: number): number[] =>
  new Array(stop - start).fill(0).map((v, i) => start + i);

First, we created a new array; then, we applied the fill() method to it, which updated the array in place (side effect) and returned the updated array, to which we finally applied a map() method. The latter method generated a new array, to which we could have applied further mapping, filtering, or any other available method.

Let’s take a look at a common...