gistfile1.txt

~ $ python
Python 2.7.10 (default, Jun  2 2015, 17:24:15)
[GCC 4.2.1 Compatible Apple LLVM 6.1.0 (clang-602.0.53)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> l = [1]
>>> d = {}
>>> d[l] = "foo"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'
>>>
~ $ node
> l = [1]
[ 1 ]
> d = new Map();
Map {}
> d.set(l, "foo");
Map { [ 1 ] => 'foo' }
> d.get(l);
'foo'
> d.keys()
{}
> d.values();
{}
> d
Map { [ 1 ] => 'foo' }
> for (k of d) { console.log(k) }
[ [ 1 ], 'foo' ]