SQLite user-defined functions

You can register custom SQLite functions on the connection using db.function(name, fn).

The fn argument is your user-defined callback:

• It is invoked by SQLite every time the SQL function is called.
• Callback arguments are positional and match the SQL call (for example, my_fn(a, b) maps to (a, b)).
• Return a SQLite-compatible scalar value (for example text, number, or null).
• Throwing inside the callback fails the SQL statement.

db.function(...) is sync-only in Node and Deno, but can be async or sync in Bun.

import map from './map';
const db = map.sqlite('demo.db');

await db.function('add_prefix', (text, prefix) => `${prefix}${text}`);

const rows = await db.query(
  "select id, name, add_prefix(name, '[VIP] ') as prefixedName from customer"
);

If you need the function inside a transaction, register it within the transaction callback to ensure it is available on that connection.

await db.transaction(async (db) => {
  await db.function('add_prefix', (text, prefix) => `${prefix}${text}`);
  return db.query(
    "select id, name, add_prefix(name, '[VIP] ') as prefixedName from customer"
  );
});

db.function(...) is available on direct SQLite connections (for example map.sqlite(...)) and not through map.http(...).