Anagram tester algoritm

anagram.js

function anagramTester(dictionary) {
  var hash = _.groupBy(dictionary, sortStr)
  return function(word) {
    var sortedWord = sortStr(word)
    return (sortedWord in hash) ? hash[sortedWord] : []
  }

  function sortStr(str) { return _.map(str, _.identity).sort().join('') }
}

var tester = anagramTester(['dog','god','cat','tag','good'])

tester('dog') //returns ["dog", "god"]
tester('cat') //returns ["cat"]
tester('foo') //returns []