I'm a newb to Javascript to this should be an easy one

I have a function with 4 variables that i want to loop through to determine if at least 1 exists. If at least 1 exists (or more) i want to return true, if none exist i want to return false. I know how to do it for just 1 variable but how can i do it with 4 in this situation? Thanks!

function seg_exists ()

var a = sega
var b = segb
var c = segc
var d = segd

if (a == undefined || a.toString().length == 0)
{ return false}

return true