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no-expression-statement

Disallow standalone expression statements.

Targeted pattern scope​

This rule targets ExpressionStatement nodes, with optional ignore patterns.

What this rule reports​

  • Top-level or block-level expression statements used only for side effects

Why this rule exists​

Expression statements often hide mutation and side effects. Explicit value flow is clearer in immutable code.

❌ Incorrect​

doWork();

✅ Correct​

const result = compute(input);

Additional examples​

// ❌ Side-effect expression statement
analytics.track("checkout_started");

// ✅ Explicit command collection
const event = {
    name: "checkout_started",
    timestamp: Date.now(),
};

return publishAnalytics(event);

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-expression-statement": "error",
        },
    },
];

When not to use it​

Disable this rule for side-effect-centric entry points such as CLI bootstrap files, telemetry initializers, or test setup scripts. Those files are intentionally imperative, and forcing expression-only style there usually adds ceremony without real safety gains.

Rule catalog ID: R904

Further reading​