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no-reflect-mutation

Disallow mutating objects through Reflect mutation APIs.

Targeted pattern scope​

This rule targets mutating static calls on Reflect that alter object state or shape.

What this rule reports​

  • Reflect.set(...)
  • Reflect.deleteProperty(...)
  • Reflect.defineProperty(...)
  • Reflect.setPrototypeOf(...)
  • Reflect.preventExtensions(...)

Why this rule exists​

Reflect mutation methods provide low-level imperative object mutation capabilities. Their usage can bypass otherwise immutable coding conventions and make state transitions difficult to track.

This rule keeps object evolution explicit by flagging mutation-centric Reflect calls.

❌ Incorrect​

const target = { value: 1 };
Reflect.set(target, "value", 2);

✅ Correct​

const target = { value: 1 };
Reflect.get(target, "value");

Additional examples​

// ❌ Removes property from existing object in place
const target = { value: 1 };
Reflect.deleteProperty(target, "value");

// ✅ Reads object metadata without mutation
const target = { value: 1 };
Reflect.ownKeys(target);

ESLint flat config example​

import immutable from "eslint-plugin-immutable-2";

export default [
    {
        files: ["**/*.{js,mjs,cjs,ts,mts,cts,tsx}"],
        plugins: { immutable },
        rules: {
            "immutable/no-reflect-mutation": "error",
        },
    },
];

When not to use it​

If your architecture depends on runtime meta-programming with controlled Reflect mutations, this rule may be too restrictive for those internal layers.

Rule catalog ID: R924

Further reading​