Hands-On Functional Programming with TypeScript

The iterator pattern

To understand how the observable sequence pattern works, we also need to understand the iterator pattern. The following code snippet uses a generator to create an iterator that iterates the multiples of a given number in an array. Only the elements in the array that are multiples of a given number are iterated:

function* iterateOnMultiples(arr: number[], divisor: number) {    for (let item of arr) {        if (item % divisor === 0) {            yield item;        }    }}

To get an instance of the iterator, we only need to invoke the function and pass an array and a number as its arguments. The function returns an iterator that will return the numbers in the array that are multiples of the given number: 3. We can invoke the iterator's next method to ...