function foo(state) {
  function bar() { return 1; }
  return state ? bar : null;
}
foo(false)  // null (bar is created but not used)
foo(true)() // 1 (bar is created and returned)

function foo(state) {
  return state ? function() { return 1; } : null;
}
foo(false)  // null (the anonymous function isn't even created)
foo(true)() // 1 (the anonymous function is created and returned)