symspell in js (https://medium.com/@wolfgarbe/1000x-faster-spelling-correction-algorithm-2012-8701fcd87a5f)

symspell.js

const { uniq, map, range, zip, mapValues, groupBy, flatMap } = require('lodash');

const expandWordToDeletions = (word) => {
  const wordArray = word.split("");
  const deletionList = map(
    range(word.length),
    i => {
      const copied = [...wordArray];
      copied.splice(i, 1);
      return copied.join("");
    }
  )
  return [word, ...deletionList];
};

const createMap = (words) => (
  mapValues(
    groupBy(
      flatMap(words, word => 
        zip(expandWordToDeletions(word), (new Array(word.length + 1)).fill(word))
      ),
      ([key, value]) => key
    ),
    listOfKeyValues => map(listOfKeyValues, ([key, value]) => value)
  )
);

const search = (word, dictionary) => {
  if (word in dictionary) return dictionary[word];
  else {
    return uniq(
      flatMap(
        expandWordToDeletions(word),
        deleteWord => dictionary[deleteWord],
      ).filter(Boolean)
    )
  }
};

const dictionary = createMap(["matt handler", "mutt handler"]);
console.log(search("patt handler", dictionary));