What is the output of this code and how it comes?

Question

var a=1;
b=a;
alert(-- a + b --);

Answer 1

makhrab dip

a = 1
So b would be 1 because b = a

Now --a is pre-decrement so a would be 0
b-- is post decrement which first assign value so b-- would be 1

So finally 0 + 1 = 1

Answer 2

Both pre and post decrement should work for substract . Both a and b supposed to be 0 and result 0. Can anyone explain ?