Why does Array.filter(Number) filter zero out in JavaScript?

Question

I\'m trying to filter all non-numeric elements out from an array. We can see the desired output when using typeof. But with Number, it filters zero out.

Here\'s the

Answer 1

The reason for this behavior is that 0, null, undefined, NaN is equivalent to false in JavaScript so, in the first case:

[-1, 0, 1, 2, 3, 4, Number(0), '', 'test'].filter(Number);

when used Number as one of the params in the filter, it returns the number itself. So when 0 is passed it returns 0 which javascript understands as false. So, it returns

[-1, 1, 2, 3, 4]

So to be on the safe side it is advised to use Number.isFinite instead of just Number.

[-1, 0, 1, 2, 3, 4, Number(0), '', 'test'].filter(Number.isFinite);

Gives same results as

[-1,0,1,2,3,4, Number(0), '','test'].filter(n=> typeof n === 'number');

would give.