I want to get weight of packages before validation button is pressed (need to execute some code with packages):

So it's getting interesting, after validation package weight's fill in, but before validation is pressed they are showed as 0.

When I click PACK000090 it show Shipping Weight with computed value, but if I restart page, computed value is reset to 0.

After page reload:

Can someone explain this behavior? Why after clicking there is computed weight and after page reload it disappear?

Also how can I get package weight before validation button is pressed? 

Thanks!