How to make a preloader for a website?

Question

JavaScript

Now I use it like this: I
load data via ajax
I insert it into the block
I scan the block for resources to load
As a result, some files are loaded twice.
But how to select resources from plain text (before inserting into a block) so as not to load twice
Resources are: just images, background in style, video, audio

Answer 1

without downloading twice, it is unlikely that it will be possible to make a preloader with a percentage display of the download progress
, everything that I found on the Internet is either a fake or a double download