This function removes duplicate from an array and returns the unduplicated array. It does not change the original array.

removeDuplicate.js

var removeDuplicate = function(a) {
  var b = a, i = 1, j, k
  while (i < b.length) {
    k = b.length
    for (j = 0; j < i; j++) {
      if (b[i] === b[j]) {
        b.splice(i,1)
        break
      }
    }
    if (k == b.length) i++
  }
  return b
}