Why is JavaScript's post-increment operator different from C and Perl?

Question

I\'m studying for an exam on JavaScript at the moment. I\'ve also got a little knowledge of C and Perl so I\'m familiar with prefix and postfix operators in all three langua

Answer 1

In C, the line

x += x--;

is undefined behaviour. It seems like your particular compiler is treating it like:

oldx = x--;
x = x + oldx

However, the ECMAScript specification does specify op= - and it gets the value of the left-hand-side before evaluating the right-hand-side.

So it would be equivalent to:

oldx = x--;
x = oldx + oldx