1 files changed, 45 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..d4b3da5f1e
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/use-includes-instead-of-indexOf.js
@@ -0,0 +1,45 @@
+/**
+ * @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";
+
+// -----------------------------------------------------------------------------
+// Rule Definition
+// -----------------------------------------------------------------------------
+
+module.exports = function(context) {
+  // ---------------------------------------------------------------------------
+  // Public
+  //  --------------------------------------------------------------------------
+
+  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, "use .includes instead of .indexOf");
+      }
+    },
+  };
+};