# `react-doctor/no-did-mount-set-state`

Derive state in getDerivedStateFromProps or initial state instead of calling this.setState in componentDidMount, which forces an extra render.

- **Status:** Active
- **Category:** State & Effects
- **Assessment:** Evidence-required risk
- **Required evidence:** source code
- **Default configuration:** Enabled
- **Default severity:** warn
- **Scope:** All supported frameworks
- **Active when:** always
- **Requirements:** react
- **Priority:** 20 (P3)
- **Source:** oxlint-plugin-react-doctor
- **Rule set:** oxlint-plugin-react-doctor 0.9.3 (prompt schema 2)
- **Documentation:** [Official documentation](https://oxc.rs/docs/guide/usage/linter/rules/react/no-did-mount-set-state)

## Validation prompt

Confirm the detector match and collect the required evidence before deciding whether an edit is warranted.

Fires on a `this.setState(...)` call (callee object must be `this`, property named exactly `setState`) located directly inside a `componentDidMount` method or class field: including calls wrapped in a single `if` block or ternary: but only when that lifecycle method lives inside a genuine React component: an ES5 `createReactClass(...)`/`React.createReactClass(...)` call, or an ES6 class extending `Component`/`PureComponent`/`React.Component`/`React.PureComponent`. In the default "allowed" mode, a `setState` buried two or more functions deep (inside a `setTimeout`, `Promise.then`, or a callback/inner function passed elsewhere) does NOT fire; only "disallow-in-func" mode flags those. A plain function or non-React class with a method named `componentDidMount` is NOT flagged, because detection requires that enclosing `createReactClass(...)` call or React-base-class extension: so the valid fixture `function Hello() { this.setState(...) }` does not trigger.

## Evidence boundary

The diagnostic proves only that the detector's modeled source pattern matched. It does not prove runtime impact, product intent, rendered failure, or that one remediation is correct.

Establish the environment, explicit repository policy, relevant exceptions, and required rendered or runtime evidence before deciding the occurrence. This page’s Assessment and Required evidence fields define the review contract.

Default severity is registry metadata. Use the occurrence's JSON severity after repository configuration when ordering real findings.

Record one outcome:

- **Confirmed failure:** The required evidence establishes the violation.
- **Rejected:** A documented exception or false-positive predicate applies.
- **Needs evidence:** Named evidence can still be collected.
- **Unavailable:** Required evidence cannot be collected in this run.
- **Waived with evidence:** An authorized, scoped exception applies to an established failure.
- **Observation:** The review records an optional tradeoff without claiming a defect.

A waiver records its scope, authority, evidence, and review or expiry condition. It is not a pass or false positive.

## Fix prompt

Apply this candidate correction only after the required evidence confirms the risk.

If the value is available from initial props, initialize it in the constructor/class-field state or derive it directly during render; do not add getDerivedStateFromProps merely to mirror props. Keep a guarded componentDidMount update when the value inherently requires a committed DOM node, subscription, or asynchronous result, and update at the point that result actually arrives. Preserve timing and behavior rather than moving the call into a callback only to evade the detector. See https://oxc.rs/docs/guide/usage/linter/rules/react/no-did-mount-set-state

## Repository-wide copy prompt

Use this only for a repository-wide pass after validating each occurrence. For one occurrence, use the occurrence-level guidance above.

````text
Fix every confirmed `react-doctor/no-did-mount-set-state` diagnostic in the current repository.

Required change:
- If the value is available from initial props, initialize it in the constructor/class-field state or derive it directly during render; do not add getDerivedStateFromProps merely to mirror props. Keep a guarded componentDidMount update when the value inherently requires a committed DOM node, subscription, or asynchronous result, and update at the point that result actually arrives. Preserve timing and behavior rather than moving the call into a callback only to evade the detector. See https://oxc.rs/docs/guide/usage/linter/rules/react/no-did-mount-set-state.

Validation before editing:
Fires on a `this.setState(...)` call (callee object must be `this`, property named exactly `setState`) located directly inside a `componentDidMount` method or class field: including calls wrapped in a single `if` block or ternary: but only when that lifecycle method lives inside a genuine React component: an ES5 `createReactClass(...)`/`React.createReactClass(...)` call, or an ES6 class extending `Component`/`PureComponent`/`React.Component`/`React.PureComponent`. In the default "allowed" mode, a `setState` buried two or more functions deep (inside a `setTimeout`, `Promise.then`, or a callback/inner function passed elsewhere) does NOT fire; only "disallow-in-func" mode flags those. A plain function or non-React class with a method named `componentDidMount` is NOT flagged, because detection requires that enclosing `createReactClass(...)` call or React-base-class extension: so the valid fixture `function Hello() { this.setState(...) }` does not trigger.

Constraints:
- Make the smallest change that fixes the root cause.
- Preserve behavior and interfaces unrelated to this diagnostic.
- Reuse existing project components, utilities, and conventions.
- Do not introduce render-phase side effects, render-phase state updates, or Hooks rule violations.
- Adapt identifiers and framework details instead of copying blindly.
- Do not disable the rule or suppress matching code.

Assessment:
- Record detector evidence, applicability facts, assumptions, missing evidence, and the rule class for this occurrence.
- Return one outcome: Confirmed failure, Rejected, Needs evidence, Unavailable, Waived with evidence, or Observation.
- A waiver records the established failure, scope, authority, evidence, and review or expiry condition. It is not a pass or false positive.

Verification:
- Run focused tests for the changed behavior.
- Run React Doctor and confirm this diagnostic no longer appears from changed code.
- Run an unfiltered scan of the affected scope before claiming no cross-category regression.
- Report the files changed and any checks you could not run.
````