Javascript doesn't throw array index out of bounds exceptions. It simply returns undefined.

Since undefined is not equal to any possible value of opposite[dir], this will always evaluate false on the first run of the loop.

it doesnt; it pushes on the first run not pop

what types can't be anticipated?

@Calgiles3 In line 4 array with directions is returned or empty array if no direction is found (instead of null). Hope it helps!

Just in case someone else runs into this confusion: minimizing i takes precedence over minimizing j. This seemed consistent to me.

How do these two TC's not contradict each other

How 2 totally different test cases with totally different approaches to solve can contradict each other?

1. You start at 7. You walk through 7's. You end up at 7. You haven't changed your altitude even once - result is 0.
2. You start at 0. At some point you have to climb up to 1. At some point you have to climb down from 1, so you can end up at 0. The result is 2.

Why is this not == 0 then?

Ask the opposite question then: why is this 0?

If you can't construct an example that gives a result of 0, you can't claim it should be 0.

Why is this not == 0 then?

For the same reason maybe? You can't get from top left corner to bottom right corner without changing altitude.

Number of climb rounds between adjacent locations is defined as difference of location altitudes (ascending or descending).

It's the difference, not their individual value ;-)

Also what does eval and Function disabling mean?

That you can't use eval or Function in your code either.

Server side JS should be like this indeed. You should get away from your comfort zone in Java and learn all the other wonderful things in life ;-)

Could you define this "JS way of coding"?

I think you should read the description again. For 209917there is only one possible answer: [29917, O, 1].

I"m very sorry, the tests cases are consistent through all languages (it is the same algorithm everywhere) and - see the top of the page - lots of guys passed the kata.

When a kata has a lot of translations it's a good idea to state which one you're having troubles with.