sort_obj.js

>  Array.prototype.sort.call(x, (a,b) => { console.log(x); return a - b; })
{ '0': 2, '1': 1, '2': 0, '3': -1, '7': -2, '8': -3, length: 9 }
{ '0': 2, '1': 1, '2': 0, '3': -1, '7': -2, '8': -3, length: 9 }
{ '0': 2, '1': 1, '2': 0, '3': -1, '7': -2, '8': -3, length: 9 }
{ '0': 2, '1': 1, '2': 0, '3': -1, '7': -2, '8': -3, length: 9 }
{ '0': 2, '1': 1, '2': 0, '3': -1, '7': -2, '8': -3, length: 9 }
{ '0': -3, '1': -2, '2': -1, '3': 0, '4': 1, '5': 2, length: 9 }

> x = [2,1,0,-1,,,-2,-3]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
>  Array.prototype.sort.call(x, (a,b) => { console.log(x); return a - b; })
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ -3, -2, -1, 0, 1, 2, <2 empty items> ]

// wtf V8
> x = [2,1,0,-1,,,-2,-3]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
> x.sort((a,b) => {console.log(x); return a - b; })
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
[ -3, -2, -1, 0, 1, 2, <2 empty items> ]
> x = [2,1,0,-1,,,-2,-3]
[ 2, 1, 0, -1, <2 empty items>, -2, -3 ]
> x.sort()
[ -1, -2, -3, 0, 1, 2, <2 empty items> ] // WTF

according to JS spec (http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf):

Because non-existent property values always compare greater than undefined property values, and undefined always
compares greater than any other value, undefined property values always sort to the end of the result, followed by nonexistent property values.