An extension of Array with some additional helper methods I wanted.

_example.js

// Example usage
var List = require('List');

// Instantiate instances using `new`
var list = new List();

// Use .add to append a one or more unique items to the list 
list.add('foo');
list.add('BAR', 'BAZ');
list.add(1, 2,2, 3,3,3, 4,4,4,4);
console.log(list); // ["foo", "BAR", "BAZ", 1, 2, 3, 4]

// Similarly, you can use .remove to drop or or more items from the list
list.remove('foo');
list.remove(2,4);
console.log(list); // ["bar", "BAR", "BAZ", 1, 3, 4]

List.js

function List () {}
List.prototype = []
List.prototype.constructor = List

List.prototype._return = function _return (val) {
  if (val.length <= 1)
    val = val[0]

  return val
}

List.prototype.add = function add () {
  var results = []

  for (var i = 0, len = arguments.length; i < len; i++) {
    if (this.indexOf(arguments[i]) === -1)
      results.push(this.push(arguments[i]))
  }

  if (results.length)
    return this._return(results)
  else
    return this.length
}

List.prototype.remove = function remove (item) {
  var results = [],
    idx = this.indexOf(item)

  if (idx !== -1)
    return this.splice(idx, 1)

  for (var i = 0, len = arguments.length; i < len; i++) {
    idx = this.indexOf(arguments[i])
    if (idx === -1)
      results.push(this.splice(idx, 1))
  }

  return this._return(results)
}

module.exports = List