merge-arrays.js

// Merge arrays into single array, removing duplicates. This version
// removes objects that are duplicates by values, not memory pointers,
// ie. `{ foo: 'bar' }` and `{ foo: 'bar' }` are seen as duplicates

function mergeArrays() {
  var args = arguments;
  var hash = {};
  var arr = [];

  for (var i = 0; i < args.length; i++) {
    for (var j = 0; j < args[i].length; j++) {
      if (hash[args[i][j]] !== true) {
        arr[arr.length] = args[i][j];
        hash[args[i][j]] = true;
      }
    }
  }

  return arr;
}

// => [1, 2, 3, 4, 5, 6, 7, 8]
console.log(
  mergeArrays(
    [1,2,3,4,5],
    [1,2,3,4,5,6],
    [1,2,3,4,5,6,7],
    [1,2,3,4,5,6,7,8]
  )
);