Re: Private properties are undefined in JS and null in AS

[Justin Mclean]

Hi,

So here’s some data for you:

In string_old.js:

var s;

for (var i = 0; i < 1e8; i++) {
    if (s == "") {
    }
}

In string.js:

var s = "";

for (var i = 0; i < 1e8; i++) {
    if (s === "") {
    }
}

time node string.js
real    0m0.246s
user    0m0.114s
sys     0m0.046s

time node string_old.js
real    0m2.496s
user    0m2.452s
sys     0m0.019s

The === and setting to “" is an order of magnitude faster (in node anyway), 
similar results with initialising to null rather than “”.

Running similar code (converted to AS ) through the chrome profiler gives 
results where setting to null and using === is faster.

It even twice as fast if you initialise the variable and compare on every time 
through the loop. So 1e8 lots = null and a === is faster than no initialisation 
and a ==.

I think what is happening currently is that because we are not initialising the 
variable it’s doing a implicit cast on every every comparison that is very 
expensive when using != and ==, using === and !== significantly speeds this up 
but then you have the issues of uninitialise strings and objects being null in 
AS and undefined in JS but it still twice as fast.

BTW I do note that we are setting ints to 0. I assume because of similar 
reasons? But it seems you were not concerned with the overhead of this?

Thanks,
Justin