React Website preloading

Hi m8! i have an hard question! I'am new in react and i need to make a website preloader. I have an assets folder, i need to read all assets, preload with a progress bar and at the end, show my website.

My first approach is to use preloadjs and hardcoding url assets, but is very mess if i have a lot of assets, do you have any ideas to do it clever and smart?

Thanks all!!