How to check if variable is not falsy but 0 passes in Javascript

Is there an elegant way to check if variable is NOT falsy but in case of 0 it passes. The issue with this way of verifying if(var !== undefined && var !== null) is that it’s long and doesn’t cover all cases like undecalred or NaN. I’m also using typescript and declare it as optional number.

Answer

You can do exactly what your first sentence asks:

if (!x && x !== 0)

means literally “if x is falsy and x is not 0”.

Also the == and != comparison operators explicitly consider null and undefined to be equal, so

if (x != null)

is true for both null and undefined. (That’s !=, not !==.)