Rediscovering JavaScript

Chapter 8

Here are the solutions to the ​Exercises​, for the Chapter 8, ​Using Inheritance​ chapter.

Exercise 1

'use strict';

class FunctionalSet extends Set {
  filter(predicate) {
    return new FunctionalSet([...this].filter(predicate));
  }

  map(mapper) {
    return new FunctionalSet([...this].map(mapper));
  }

  reduce(accumulator, identity) {
    return [...this].reduce(accumulator, identity);
  }
}

const set = new FunctionalSet(['Jack', 'Jill', 'Tom', 'Jerry']);

const jSet = set.filter(name => name.startsWith('J'));
const allCaps = set.map(name => name.toUpperCase());

const totalLengthOfJWords =
  set.filter(name => name.startsWith('J'))
 .reduce((total, word) => total + word.length, ...