0,1,2,3
1,2,3
1,2,3
4
0,1,2,3
a,b,c,0,1,2,3
1
1
2
2
1
3
undefined
0
3
2
4
5
5
5
6
7
2
3
undefined
undefined
0
3
3
3
--- unshift 0
3
100,101,102
--- unshift 1
RangeError : Array length must be assigned a finite positive integer
length: 4294967295
  0: 200
  1: 201
  2: 202
  3: 203
  4294967294: 100
  4294967295: 101
  4294967296: 102
  4294967298: 104
  4294967299: 109
Test: unshift should throw when length is not writable.
e instanceOf TypeError = true
a.length = 1