1 files changed, 50 insertions, 0 deletions
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-includes-instead-of-indexOf.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-includes-instead-of-indexOf.js
new file mode 100644
index 0000000000..99a04bbb72
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-includes-instead-of-indexOf.js
@@ -0,0 +1,50 @@
+/**
+ * @fileoverview Use .includes instead of .indexOf
+ *
+ * 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";
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/use-includes-instead-of-indexOf.html",
+    },
+    schema: [],
+    type: "suggestion",
+  },
+
+  create(context) {
+    return {
+      BinaryExpression(node) {
+        if (
+          node.left.type != "CallExpression" ||
+          node.left.callee.type != "MemberExpression" ||
+          node.left.callee.property.type != "Identifier" ||
+          node.left.callee.property.name != "indexOf"
+        ) {
+          return;
+        }
+
+        if (
+          (["!=", "!==", "==", "==="].includes(node.operator) &&
+            node.right.type == "UnaryExpression" &&
+            node.right.operator == "-" &&
+            node.right.argument.type == "Literal" &&
+            node.right.argument.value == 1) ||
+          ([">=", "<"].includes(node.operator) &&
+            node.right.type == "Literal" &&
+            node.right.value == 0)
+        ) {
+          context.report({
+            node,
+            message: "use .includes instead of .indexOf",
+          });
+        }
+      },
+    };
+  },
+};