diff --git a/README.md b/README.md
index bde015a9..b7b06255 100644
--- a/README.md
+++ b/README.md
@@ -82,14 +82,24 @@ export default [...common, ...modules, ...node, ...prettier];
 <summary>Extending rules</summary>
 <br>
 
-```js
-import { common, modules, node, stylistic, typescript } from "@hazmi35/eslint-config";
+Extending rules using the extend function is recommended.
 
-export default [...common, ...modules, ...node, ...stylistic, ...typescript, {
-    rules: {
-        "@typescript-eslint/no-unnecessary-condition": "off"
+```js
+import { common, extend, modules, node, stylistic, typescript } from "./index.js";
+
+export default [...common, ...modules, ...node, ...stylistic, ...extend(typescript, [
+    {
+        rule: "@typescript-eslint/no-unnecessary-condition",
+        option: [
+            "warn",
+            {
+                allowConstantLoopConditions: false
+            }
+        ]
+        // or
+        option: "off"
     }
-}];
+])];
 ```
 </details>
 
diff --git a/index.js b/index.js
index fcd90bd3..ed3c9b88 100644
--- a/index.js
+++ b/index.js
@@ -6,3 +6,20 @@ export { default as node } from "./conf/node.js";
 export { default as prettier } from "./conf/prettier.js";
 export { default as stylistic } from "./conf/stylistic.js";
 export { default as typescript } from "./conf/typescript.js";
+
+/**
+ * @param {import("eslint").Linter.FlatConfig[]} config
+ * @param {{ rule: string, option: ["off" | "warn" | "error", object] }[]} rulesAndOptions
+ * @returns {import("eslint").Linter.FlatConfig[]}
+ * @example extend(config, [{ rule: "no-console", option: ["warn", { allow: ["warn", "error"] }] }])
+ */
+export function extend(config, rulesAndOptions) {
+    return config.map(c => {
+        if (c.rules) {
+            for (const { rule, option } of rulesAndOptions) {
+                c.rules[rule] = option;
+            }
+        }
+        return c;
+    });
+}