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no-loop-statement

Disallow imperative loop statements.

Targeted pattern scope​

This rule targets for, for..in, for..of, while, and do..while statements.

What this rule reports​

  • Loop statements that mutate control flow imperatively

Why this rule exists​

Declarative transforms (map, filter, reduce) are usually easier to reason about in immutable systems.

❌ Incorrect​

for (const item of items) {
  sum += item;
}

✅ Correct​

const sum = items.reduce((acc, item) => acc + item, 0);

Additional examples​

// ❌ Imperative loop with mutable accumulator
let totalByUser = 0;
for (const order of orders) {
  if (order.userId === currentUserId) {
    totalByUser += order.total;
  }
}

// ✅ Composed filter + reduce pipeline
const totalByUser = orders
  .filter((order) => order.userId === currentUserId)
  .reduce((sum, order) => sum + order.total, 0);

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

When not to use it​

Loops can be the clearest option for early exits, streaming parsers, and certain performance-sensitive hotspots. If your team intentionally uses for loops in those places, scope-disable this rule there and keep it active elsewhere.

Rule catalog ID: R906

Further reading​