a=Array(b,c,d,e)
(4) [Array(3), Array(3), Array(3), Array(3)]
0: (3) [3, 2, 1]
1: (3) [2, 1, 2]
2: (3) [5, 5, 5]
3: (3) [7, 7, 7]
length: 4
__proto__: Array(0)
a.sort(function(a,b) {
return Math.random() - 0.5
});
(4) [Array(3), Array(3), Array(3), Array(3)]
0: (3) [5, 5, 5]
1: (3) [2, 1, 2]
2: (3) [3, 2, 1]
3: (3) [7, 7, 7]
length: 4
__proto__: Array(0)