Preloader and overlay with javascripting.

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Javascript

I have an html page with two section.
left section is tree with many knots, default with one and rest are appearing after clicking +
by clicking each knots the related page will be displayed in the right section.
Right section data itself has many internal links.
Loading time is varying depends on the data to be loaded.
Problems now:
There is no pre loader in both section or general.
Solution I needed
1. Display a preloader and an element overlay on the left section to prevent the user interaction till the data loaded in the right section
2. Display a preloader and an element overlay on the right section till the page/data fully loaded here to prevent the user to interact with partly displayed items.

What I have tried:

trying with css preloader, working locally but not working in server