Why does Math.min() return positive infinity, while Math.max() returns negative infinity?

Of course it would, because the start number should be Infinity for Math.min. All number that are lower than positive infinity should be the smallest from a list, if there are no smaller.

And for Math.max it’s the same; all numbers that are larger than negative infinity should be the biggest if there are no bigger.

So for your first example:

Math.min(5) where 5 is smaller than positive infinity (Infinity) it will return 5.

Update

Calling Math.min() and Math.max with an array parameter may not work on every platform. You should do the following instead:

Math.min.apply(null, [ 1, 2, 3, 4 , 5 ]);

Where the first parameter is the scope argument. Because Math.min() and Math.max() are “static” functions, we should set the scope argument to null.