Question

I admit that I asked a question about why Closure Compiler does not shorten certain code which looks shortenable at first sight a few days ago already, but that reason is not applicable in this case and I’m not really sure why it isn’t shortened here.

What code I have is:

var a = 0;
function b() {
    return a++ >= 3;
}

Now there is pre-incrementing and post-incrementing. The difference is the return value – a++ returns a and then increments it, ++a first increments a and then returns it.

What this comes down to is that my code could be shortened to (ignoring whitespace removal):

var a = 0;
function b() {
    return ++a > 3;
}

However, Closure Compiler does not seem to alter (or recognise) this.

My question therefore is: what side effects could ++a > have when used instead of a++ >=?

Answer 1

There is a particular edge-case for this construct (but not for 3).

It occurs because JavaScript stores numbers as IEEE-754 float-point 64-bit doubles and “only” has a guaranteed “exact” integer-representation up to 2^53 (although implementations may have lee-way to have a higher range, I do not know).

This is on Firefox 4:

a = 2e53
a++ >= 2e53 // true

a = 2e53
++a > 2e53 // false

Real question is what realized gain would such a very particular transformation have? :-0

Happy coding.