What’s the best way to read Sqlite3 directly in Browser using Javascript?

There is a javascript library called sql.js that can do exactly what you want. In your case, you would use it like that

const SQL = await initSqlJs(options);
const fetched = await fetch("/path/to/database.sqlite");
const buf = await fetched.arrayBuffer();
const db = new SQL.Database(new Uint8Array(buf));
const contents = db.exec("SELECT * FROM my_table");
// contents is now [{columns:['col1','col2',...], values:[[first row], [second row], ...]}]

See the documentation on sql-js.github.io/sql.js/documentation/