I have a lot of data that needed to be loaded on one page. It always takes a long time. How can I display a message page while this data page is loading and then display the data page after the data is completely loaded? Do you have any examples?

I tried to use the <META> function. There are two problems I had:
One, The message page was displayed but the data page did not start to load the data until it is displayed, even I set up a delay time on the message page.

Second, to load the data page, I have to provide the complete URL, which is not convenient for us, since it needs to be moved to a different URL. We do not want to have a hard-code in the program. How can I just give the program name and the same relative path instead of the URL?

Thanks in advance.