My attempt to write an anagram finder function in Node by using functional programming paradigms.

findAnagrams.js

const words = require('an-array-of-english-words');

const findAnagrams = (word, allWords) => {
  const letters = word.split('')

  const getNumberOfLetters = anArray => anArray.reduce((acc, letter) => ({
    ...acc,
    [letter]: acc[letter] ? acc[letter] + 1 : 1,
  }), {});

  const letterNumbers = getNumberOfLetters(letters);

  return allWords
    .filter(someWord => someWord.length === word.length)
    .filter(someWord => {
      const someWordLetterNumbers = getNumberOfLetters(someWord.split(''));
      return Object.keys(someWordLetterNumbers).every(someLetter => someWordLetterNumbers[someLetter] === letterNumbers[someLetter] && someWord !== word);
    });
}