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/

I can not tell the best, but one: Write a JavaScript SQLite reader library yourself. This will be a tedious task, but I am sure it can be done. Some cool folks have done pdf.js, which is a JavaScript renderer for PDF files, which are also binary BLOB's like SQLite files are.

You will most probably start with the FileReader API to walk thru the SQLite file, then create some in-memory representation of the content, which your chart tool can use.

Disclaimer: You probably want to solve your initial problem with another solution, as proposed by others, but this answers your question.