Why does the code outputs 124 instead of 125?

Question

var a = 0;
for (b=1; b<=5; b+=a) {
document.write(b);
a++;
}

Answer 1

a = 0
b = 1
b <= 5 ? => true
Begin loop:
write b <= 1
a = a + 1 <= 1
b = b + a <= 2
b <= 5 ? => true
Iter loop:
write b <= 2
a = a + 1 <= 2
b = b + a <= 4
b <= 5 ? => true
Iter loop:
write b <= 4
a = a + 1 <= 3
b = b + a <= 7
b <= 5 ? => false

Output: 124

Answer 2

The loop increases in this sequence 1, 2, 3 adding to the resulted number the final number in the loop is 7 hence the loop stops...so the output will result i 124 there is no where in the loop we can get 125 cause 5 will be no where seen in the set of resulted numbers

Answer 3

But Diego I don't see any condition in the loop where b==0

Answer 4

In each loop, "a" increases by 1. After each loop, "b" increases by "a".

1. b == 1.
a++ // a == 1

2. b == a+b == 1+1 == 2.
a++ // a == 2

3. b == a+b == 2+2 == 4.
a++ // a == 3

4. b == a+b == 3+4 == 7
Condition "b <= 5" is False so loop stops.

EDIT: Variable "b" equals 1 at the beginning, not 0.

Answer 5

Because 2+2==4 and not 5.