Add lua-multi-incr.js example (#1692)

Also fix syntax error in the lua example in the README

Closes #1689.

README.md

@@ -209,9 +209,9 @@ import { createClient, defineScript } from 'redis';
       add: defineScript({
         NUMBER_OF_KEYS: 1,
         SCRIPT:
-          "local val = redis.pcall('GET', KEYS[1]);' + 'return val + ARGV[1];",
+          "local val = redis.pcall('GET', KEYS[1]);" + "return val + ARGV[1];",
         transformArguments(key: string, toAdd: number): Array<string> {
-          return [key, number.toString()];
+          return [key, toAdd.toString()];
         },
         transformReply(reply: number): number {
           return reply;

examples/README.md

@@ -3,8 +3,9 @@
 This folder contains example scripts showing how to use Node Redis in different scenarios.
 
 | File Name                | Description                                                                   |
-|--------------------------|--------------------------------------|
+| ------------------------ | ----------------------------------------------------------------------------- |
 | `connect-as-acl-user.js` | Connect to Redis 6 using an ACL user                                          |
+| `lua-multi-incr.js`      | Define a custom lua script that allows you to perform INCRBY on multiple keys |
 
 ## Contributing
 

examples/lua-multi-incr.js

@@ -0,0 +1,31 @@
+// Define a custome lua script that accepts two keys and an amount to
+// increment each of them by
+
+import { createClient, defineScript } from 'redis';
+
+async function luaMultiIncr() {
+  const client = createClient({
+    scripts: {
+      mincr: defineScript({
+        NUMBER_OF_KEYS: 2,
+        SCRIPT:
+          'return {' +
+          'redis.pcall("INCRBY", KEYS[1], ARGV[1]),' +
+          'redis.pcall("INCRBY", KEYS[2], ARGV[1])' +
+          '}',
+        transformArguments(key1, key2, increment) {
+          return [key1, key2, increment.toString()];
+        },
+      }),
+    },
+  });
+
+  await client.connect();
+
+  await client.set('mykey', '5');
+  console.log(await client.mincr('mykey', 'myotherkey', 10)); // [ 15, 10 ]
+
+  await client.quit();
+}
+
+luaMultiIncr();