diaplay html page before executing js code

[max]

Hi,

I've developed some HTML pages with js language.
In one of the pages, I execute some functions which take a long time
when the page is charging.
So, the page is displayed after all the code is executed. So, during
the code is executed, the previous page continues to be displayed.
So, is there any way to force the page to be displayed before the js
code is executed ???

Many thanks in advance for your help.