http://www.freecodecamp.com/dannycoder 's solution for Bonfire: Sorted Union

bonfire-sorted-union#.js

// Bonfire: Sorted Union
// Author: @dannycoder
// Challenge: http://www.freecodecamp.com/challenges/bonfire-sorted-union#
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function unite(arr1, arr2, arr3) {
  var newArray = [];
  
  for(var i = 0; i < arguments.length; i++) {
    for (var j = 0; j < arguments[i].length; j++)
      {
        //add first element to array
        if( i === 0 && j === 0) {
          newArray.push(arguments[i][j]);
          continue;
        }        
        //add next element if not found in the @newArray
        if(newArray.indexOf(arguments[i][j]) === -1){
          newArray.push(arguments[i][j]);
          console.log(arguments[i][j]);
        }        
      }
  }
  return newArray;
}

unite([1, 3, 2], [5, 2, 1, 4], [2, 1]);