find_anagrams.js

const words = ['map', 'art', 'how', 'rat', 'tar', 'who', 'pam', 'shoop'];

const sortWord = (word) => (
  word.split('').sort().join('')
);

const matches = words.reduce((obj,w) => {
  if (w) {
    const k = sortWord(w);
    if (!(k in obj)) {
      obj[k] = [];
    }

    obj[k].push(w);
  }
  
  return obj;
}, {});

console.log(matches);