What does line 10,12 and 13 do and why?

Consider this Javascript code: A Nm 1. var a; 2. function foo () { 3. var b; 4. function bar() { 5. a = 1; 6. } 7. bar(); 8. } 9. 10. console.log(a); 11. foo(); 12. console.log(a); 13. console.log(b)