remove duplicates from array

gistfile1.txt

const names = ['Mike', 'Matt', 'Nancy', 'Adam', 'Jenny', 'Nancy', 'Carl']

const count = names => 
  names.reduce((a, b) => 
    Object.assign(a, {[b]: (a[b] || 0) + 1}), {})

const duplicates = dict => 
  Object.keys(dict).filter((a) => dict[a] > 1)

console.log(count(names)) // { Mike: 1, Matt: 1, Nancy: 2, Adam: 1, Jenny: 1, Carl: 1 }
console.log(duplicates(count(names))) // [ 'Nancy' ]

http://stackoverflow.com/questions/840781/easiest-way-to-find-duplicate-values-in-a-javascript-array