Are you referring to a case like this? { f(); var a = 3; function f() { console.log(a); } } That will print "undefined

Are you referring to a case like this? { f(); var a = 3; function f() { console.log(a); } } That will print "undefined" because the entire function f() is hoisted and callable in the first line, but the variable a has not yet been assigned the value. That's not a race condition (those are related to timing in concurrent systems) but is certainly the sort of counter-intuitive visibility that makes me prefer to use function expressions most of the time.