HTML5: Add a 'begin download' button?

My packaged app is working in a browser, but because of the size I would like to create a splash screen quickly explaining what the app does etc, rather than beginning to load the app as soon as the site is launched.

I have tried wrapping the .web.UE4.js file in a function that starts on a button click, but the loading doesn’t complete. Debugger says it gets stuck on the dependency ‘wait-for-compiled-code’.

Has anyone had any success with a launch button (importantly that begins the download, not plays the game after the download is complete)? I’m not great with coding.

Thanks