Method chaining

Chain them all

// Let's count vowels in a string using the method chaining
const VOWELS = ['a', 'e', 'i', 'o', 'u'];

// Reduce an array of letters to get the sum of vowels
// and pass a function to .reduce method to make it more readable
const countVowels = (sum, letter) => (VOWELS.includes(letter) ? ++sum : sum);

// 1. .replace returns a string without whitespaces
// 2. .split returns an array of letters
// 3. .reduce reduces an array of letters into a single number - the sum of vowels
const getVowelsCount = (string) =>
  string.replace(/ /g, '').split('').reduce(countVowels, 0);

Summary

• Method chaining is a really good pattern for avoiding repetition and making your code more readable.
• It plays well with functional programming and is often used in JavaScript.
• Each of the methods needs to return something in order to call another method on it. Hence the chaining name.