docs: add createCallbackFunction page

docs/.vitepress/config.ts

@@ -31,6 +31,10 @@ export default defineConfig({
 						text: 'transaction',
 						link: '/api/transaction',
 					},
+					{
+						text: 'createCallbackFunction',
+						link: '/api/createcallbackfunction',
+					},
 					{
 						text: 'getDatabaseFile',
 						link: '/api/getdatabasefile',

docs/api/createcallbackfunction.md

@@ -0,0 +1,48 @@
+# createCallbackFunction
+
+Create a SQL function that can be called from queries to trigger a JavaScript callback.
+
+## Usage
+
+Access or destructure `createCallbackFunction` from the `SQLocal` client.
+
+```javascript
+import { SQLocal } from 'sqlocal';
+
+export const { createCallbackFunction } = new SQLocal('database.sqlite3');
+```
+
+<!-- @include: ../_partials/initialization-note.md -->
+
+This method takes a string to name a custom SQL function as its first argument and a callback function as its second argument which the SQL function will call. After running `createCallbackFunction`, the function that you defined can be called from subsequent SQL queries. Arguments passed to the function in the SQL query will be passed to the JavaScript callback.
+
+A good use-case for this is making SQL triggers that notify your application when certain mutations are made in the database. For example, let's create a `logInsert` callback function that takes a table name and a record name to log a message.
+
+```javascript
+await createCallbackFunction('logInsert', (tableName, recordName) => {
+	console.log(`New ${tableName} record created with name: ${recordName}`);
+});
+```
+
+Then, we can create a temporary trigger that calls `logInsert` whenever we insert a row into our `groceries` table.
+
+```javascript
+await sql`
+  CREATE TEMP TRIGGER 'logGroceriesInsert' AFTER INSERT ON groceries
+  BEGIN
+    SELECT logInsert('groceries', new.name);
+  END
+`;
+```
+
+Now, a message will be automatically logged whenever a query on the same connection inserts into the `groceries` table.
+
+```javascript
+await sql`INSERT INTO groceries (name) VALUES ('bread')`;
+```
+
+```log
+New groceries record created with name: bread
+```
+
+Note that each callback function that you create will be connection-specific. If you create more than one connection using additional `SQLocal` instances but want to use the same function in queries sent over the other connections as well, you will need to call `createCallbackFunction` on each instance.