From 5f1f5bd291209246f2351d9597481b4aa761d513 Mon Sep 17 00:00:00 2001
From: Kristjan ESPERANTO <35647502+KristjanESPERANTO@users.noreply.github.com>
Date: Mon, 13 Oct 2025 23:40:23 +0200
Subject: [PATCH] feat: add ESlint rule `no-sparse-arrays` for config check
 (#3911)
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Adding a rule to the config checker config so that unexpected commas in
the middle of arrays (reported in issue #3910) are better detected.

Two commas in a row inside the modules array create an empty entry
(`undefined`). JavaScript accepts that syntax, but MagicMirror would
later try to load that “module” and fail.

Alternatively, we could filter out undefined entries, but with this PR,
the user receives a clear message indicating where the error lies, can
easily fix it, and thus has a cleaner configuration.

## Before

```
[2025-10-10 19:33:30.874] [INFO]  Checking config file /home/kristjan/MagicMirror/config/config.js ...
[2025-10-10 19:33:30.944] [INFO]  Your configuration file doesn't contain syntax errors :)
[2025-10-10 19:33:30.945] [INFO]  Checking modules structure configuration ...
[2025-10-10 19:33:31.027] [ERROR] This module configuration contains errors:
undefinedmust be object
```

## After

```
[2025-10-10 19:41:20.030] [INFO]  Checking config file /home/kristjan/MagicMirror/config/config.js ...
[2025-10-10 19:41:20.107] [ERROR] Your configuration file contains syntax errors :(
Line 91 column 1: Unexpected comma in middle of array.
```
---
 CHANGELOG.md       | 2 ++
 js/check_config.js | 5 ++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 797cb57a..404fdc98 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,8 @@ planned for 2026-01-01
 
 ### Fixed
 
+- feat: add ESlint rule `no-sparse-arrays` for config check to fix #3910 (#3911)
+
 ### Updated
 
 - [core] Update dependencies (#3909)
diff --git a/js/check_config.js b/js/check_config.js
index 14fda3c5..d8c97358 100644
--- a/js/check_config.js
+++ b/js/check_config.js
@@ -58,7 +58,10 @@ function checkConfigFile () {
 					...globals.node
 				}
 			},
-			rules: { "no-undef": "error" }
+			rules: {
+				"no-sparse-arrays": "error",
+				"no-undef": "error"
+			}
 		},
 		configFileName
 	);