How to turn on "FTS3", "spatialite" extension?

I read all those below, but it is still for me impossible to do it.
Too hard for many people like me.

Can you provide a guide or document details how to include FTS3 and spatialite extension?

a step by step guide will make us easier.

Or simple just provide a final build result and published it here for download, that will be great!

Look for "load extension", "FTS3", "spatialite" in the existing issues:

https://github.com/sql-js/sql.js/issues/68
https://github.com/sql-js/sql.js/issues/89
https://github.com/sql-js/sql.js/issues/316#issuecomment-569073185
https://github.com/sql-js/sql.js/issues/342#issuecomment-587336036

Originally posted by @frafra in https://github.com/sql-js/sql.js/issues/390#issuecomment-623519922

Start by reviewing the linked issues 68, 89, 316, and 342, which contain the existing discussion of loadable extensions, FTS3, and spatialite. Clarify whether the intended deliverable is a step-by-step guide or a downloadable build, then make the chosen process reproducible and verify that it covers both requested extensions.