Javascript files are loaded asynchronously which can change the order of the evaluation of "script" elements in the updated page.

Will it be possible for us to load the JavaScript files asynchronously, but execute them only in page order?

That will still require a blocking/waiting mechanism to guarantee the order of execution.

Get JS files synchronously to guarantee the order of evaluation of script elements in the page.

What are the performance implications of loading JS files synchronously?

When the JS files are loaded the first time (not cached) the user will maybe notice a delay for the updates to be applied. The delay will depend on factors like connection speed and size of files.

We believe this to be the correct behavior as it is important that all JavaScript functions are available before the user interacts with the page (potentially invoking JavaScript functions in event handlers). Loading the JavaScript resources synchronously blocks the UI thread until the resources are loaded. If the browser is implemented correctly, they will have separate UI threads for separate windows.