Why's this 04 & not 02?

Question

for(i = 0; i < 5; i++) {
i += i;
document.write(i);
i++;
}

Answer 1

i += i means i = i+i
i++ mean increase by 1
So, 1st time:
i = 0+0
write 0.
i become 1.
Then increase by 1 (which is in for loop).
so i become 2 (condition is still true).
So, 2nd time:
i = 2 + 2
write 4.
i become 5.
Then increase by 1 in for loop.
So i become 6.
Then condition is false.

Output is 04

Answer 2

In the for loop, it will automatically increment the variable being tested within the brackets, based on the third condition given (in this case it bring i++). Because you're incrementing i twice (once within the loop and once for the actual loop), the second iteration returns i as 2, which gets added to itself, therefore resulting in it being 4.