index.js

var _ = require("lodash");

var WordNet = require("node-wordnet");
var wordnet = new WordNet({cache:true});

var isLetter = function(c) {
  return c.toLowerCase() != c.toUpperCase();
};

var _findForms = function(input) {
  var i, wordforms = [], word, _ref, reducer;

  reducer = function(list) {
    return _.reduce(list, function(memo, word){
      return (memo.length < word.length) ? memo : word;
    });
  };

  if (isLetter(input.charAt(0))) {
    return wordnet.validFormsAsync(input).then(function(results) {
      if (results && results.length !== 0) {
        for (i = 0; i < results.length; i++ ) {
          _ref = results[i].split('#');
          word = _ref[0];
          wordforms.push(word);
        }
        return reducer(_.uniq(wordforms));
      } else {
        return [input];
      }
    });
  } else {
    return [input];
  }
};

exports.lemmatize = function(input, cb) {
  var lookup;

  if(_.isString(input)) {
    lookup = [input]; // Assuming a single word.
  } else if (_.isArray(input)) {
    lookup = input;
  } else {
    lookup = [];
  }

  return Promise.all(lookup.map(_findForms)).then(function(res) {
    res = _.flatten(res);
    if (cb) {
      cb(null, res);
    }
    return res;
  });
};