What does these codes do ?

Question

var a = 1; var num = [2, 3, 4, 5, 6, 7, 8];
console.log(num[a++]);

and
var a = 1; var num = [2, 3, 4, 5, 6, 7, 8];
console.log(num[++a]);

Answer 1

a = 1
a++ => 1
num[1] => 3

a = 1
++a => 2
num[2] => 4

pre increment
post increment