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no-class

Disallow class declarations and expressions.

Targeted pattern scope​

This rule targets class syntax in declarations and expressions.

What this rule reports​

  • class Name {} declarations
  • const X = class {} expressions

Why this rule exists​

Class instances often rely on mutable state. Functional composition with plain objects is easier to keep immutable.

❌ Incorrect​

class Counter {
  value = 0;
}

✅ Correct​

const createCounter = () => ({ value: 0 });

Additional examples​

// ❌ Class expression keeps mutable instance state
const Store = class {
    private cache = new Map<string, string>();
};

// ✅ Factory returns explicit values and functions
const setEntry = (
    cache: ReadonlyMap<string, string>,
    key: string,
    value: string,
) => new Map([...cache.entries(), [key, value]]);

const createStore = (cache: ReadonlyMap<string, string> = new Map()) => ({
    get: (key: string) => cache.get(key),
    set: (key: string, value: string) => createStore(setEntry(cache, key, value)),
});

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-class": "error",
    },
  },
];

When not to use it​

You may disable this rule in framework layers that require class-based APIs (for example older React class components, some decorator-driven DI frameworks, or inheritance-heavy SDK extension points). A practical compromise is enabling no-class for application code while carving out a narrow override for those integration folders.

Rule catalog ID: R902

Further reading​