if a.length is 0, then it would be considered falsey (any of: 0, null, NaN, false, '', undefined) and it would jump to the next condition (b.length) and so on until it finds a truthy value OR hitting variable c which is 0 (considered falsey again), ending/never starting the while loop.

for the ~~ operators, it's a binary operator, called bitwise NOT. It will invert the bits of undefined, making it be -1, then inverting again (~~) and being 0.

source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Bitwise_NOT

|| is a OR comparison, if any conditions are true, it will evaluate as true.

i.e.
(false || false || true) == true;