Questions

The size of the pupil of the eye automatically adjusts itself  according to the intensity of light passing through it;if the intensity is more , the size is less, if less, it is more. So in our case the pupil should dilate i.e, increase in size to be able to see in the dark . This switchover takes sometime. But here the entry into the dark room is immediate . So the eye has no time to adjust itself and hence is not able to see at all for a while.

The Math.floor() function in JavaScript is used to round off the number passed as parameter to its nearest integer in Downward direction of rounding i.g towards the lesser value.

Hence, math.floor(3.6) = 3.