1 files changed, 42 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/var-only-at-top-level.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/var-only-at-top-level.js
new file mode 100644
index 0000000000..5da799c643
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/var-only-at-top-level.js
@@ -0,0 +1,42 @@
+/**
+ * @fileoverview Marks all var declarations that are not at the top level
+ *               invalid.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+"use strict";
+
+var helpers = require("../helpers");
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/rules/var-only-at-top-level.html",
+    },
+    messages: {
+      unexpectedVar: "Unexpected var, use let or const instead.",
+    },
+    schema: [],
+    type: "suggestion",
+  },
+
+  create(context) {
+    return {
+      VariableDeclaration(node) {
+        if (node.kind === "var") {
+          if (helpers.getIsTopLevelScript(context.getAncestors())) {
+            return;
+          }
+
+          context.report({
+            node,
+            messageId: "unexpectedVar",
+          });
+        }
+      },
+    };
+  },
+};