This is def clever but not best practice. Never do this in real code. This is not readable. Not maintanable. Not extensible.

Actually it should be [ 42 ]

I don't know how it is passed. But in test section there is wrong expected values. And this is very missleading in fail report.

For those who did not finish this kata yet, correct messages are:

"Oh no! It was fooled by Array.prototype['42']" Expected value [ 10 ]
"Oh no! It was fooled by Array.prototype['3']" Expected value [ 42 ]