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no-throw

Disallow throw statements.

Targeted pattern scope​

This rule targets ThrowStatement nodes.

What this rule reports​

  • Any direct throw statement

Why this rule exists​

Value-level error handling (for example Result/Either patterns) can be easier to model and compose.

❌ Incorrect​

throw new Error("fail");

✅ Correct​

return { ok: false, error: "fail" };

Additional examples​

// ❌ Throwing during parsing
const parsePort = (value: string) => {
    const port = Number(value);
    if (!Number.isInteger(port) || port <= 0) {
        throw new Error("Invalid port");
    }
    return port;
};

// ✅ Returning explicit parse outcome
const parsePort = (value: string) => {
    const port = Number(value);
    if (!Number.isInteger(port) || port <= 0) {
        return { ok: false, error: "Invalid port" };
    }
    return { ok: true, value: port };
};

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

When not to use it​

If your runtime model depends on exceptions (for example framework error boundaries, startup-fail-fast behavior, or assertion libraries), enforcing no-throw everywhere can be counterproductive. Prefer restricting this rule to business logic layers where value-based error handling is a goal.

Rule catalog ID: R911

Further reading​