Adds example for mixing arbitrary and supported commands in a transaction context. (#2315)

* Adds example for transactions with arbitrary commands.

* Formatting.

* Update transaction-with-arbitrary-commands.js

Co-authored-by: Leibale Eidelman <me@leibale.com>

examples/transaction-with-arbitrary-commands.js

@@ -0,0 +1,40 @@
+// How to mix and match supported commands that have named functions with 
+// commands sent as arbitrary strings in the same transaction context.
+// Use this when working with new Redis commands that haven't been added to 
+// node-redis yet, or when working with commands that have been added to Redis
+// by modules other than those directly supported by node-redis.
+
+import { createClient } from 'redis';
+
+const client = createClient();
+
+await client.connect();
+
+// Build some data fixtures.
+await Promise.all([
+  client.hSet('hash1', { name: 'hash1', number: 1}),
+  client.hSet('hash2', { name: 'hash2', number: 1}),
+  client.hSet('hash3', { name: 'hash3', number: 3})
+]);
+
+// Outside of a transaction, use sendCommand to send arbitrary commands.
+await client.sendCommand(['hset', 'hash2', 'number', '3']);
+
+// In a transaction context, use addCommand to send arbitrary commands.
+// addCommand can be mixed and matched with named command functions as
+// shown.
+const responses = await client
+  .multi()
+  .hGetAll('hash2')
+  .addCommand(['hset', 'hash3', 'number', '4'])
+  .hGet('hash3', 'number')
+  .exec();
+
+// responses will be:
+// [ [Object: null prototype] { name: 'hash2', number: '3' }, 0, '4' ]
+console.log(responses);
+
+// Clean up fixtures.
+await client.del(['hash1', 'hash2', 'hash3']);
+
+await client.quit();