When I run the js code in chrome‘s console,but I get different print

Question

The print is different,why?

the first part, I get 1,2

var a = 1;
console.log(a);
function a(){}
a = 2;
console.log(a);

the second part,I get two function a(){}

var a = 1;
if(true){
  console.log(a);
  function a(){}
  a = 2;
}
console.log(a);