is there some method of array like set in python?

Question

As I know in python i can set a list to a unique list like:

In [12]: a=range(12)

In [13]: a.append(5)

In [14]: a.append(4)

In [15]: a.append(5)

In [16]: a
Out[16]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 5, 4, 5]

In [17]: set(a)
Out[17]: set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11])

it is very useful for some scene, i just want to know how to this in javascript,

Answer 1

Javascript does not have the notion of sets. However, you can use a side effect of the fact that objects cannot have duplicate property names to replicate the functionality of a set, as seen on this blog article about the topic.

From the article:

var your_array = ['a', 'a', 'a', 'b', 'b'],
    set = {};
for (var i = 0; i < your_array.length; i++)
   set[your_array[i]] = true;
list = [];
for (var item in set)
   list.push(item);

EDIT in 2017: This is no longer true, JS got set support! MDN Docs

empty_set = new Set()
three_element_set = new Set([1, 1, 1, 2, 2, 3])
three_element_set.add(3) // still three element set

Answer 2

No, there isn't. JS is pretty basic, you have to either do it yourself or find a library where someone else has already done it.

The standard way to do this is usually insert elements into a hash, then collect the keys - since keys are guaranteed to be unique. Or, similarly, but preserving order:

function uniq(arr) {
  var seen = {}, result = [];
  var len = arr.len;
  for (var i = 0; i < len; i++) {
    var el = arr[i];
    if (!seen[el]) {
      seen[el] = true;
      result.push(el);
    }
  }
  return result;
}