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

> Disallow `this.setState()` in `componentDidMount`

`componentDidMount` runs right after the first render. Calling `setState` there renders the component a second time before the user sees anything, so every mount costs two renders. Put the value in the initial state if you already know it.

A `setState` in a callback inside `componentDidMount` is allowed by default, because it runs later, when a request finishes or an event fires.

The rule reports nothing if `settings.react.version` (`[lint.settings.react]` in `bunfig.toml`, or `settings` in an ESLint config) is 16.3 or later, or if it's `"detect"` and the installed version is 16.3 or later.

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. To turn it on:

```toml bunfig.toml
[lint.rules]
"react/no-did-mount-set-state" = "error" # or "warn"
```

Every option, set to its default. The ones that are commented out are unset by default.

```toml bunfig.toml
[lint.rules]
"react/no-did-mount-set-state" = [
  "error",
  # "disallow-in-func",
]
```

{/* End of the generated section. */}

## Examples

Reported:

{/* bad */}
```jsx
class Profile extends React.Component {
  componentDidMount() {
    this.setState({ name: this.props.name.toUpperCase() });
  }
}
```

Not reported:

{/* good */}
```jsx
class Profile extends React.Component {
  state = { name: this.props.name.toUpperCase() };

  componentDidMount() {
    loadUser(this.props.id).then(user => {
      this.setState({ user });
    });
  }
}
```

## Options

| Option | What it does |
| --- | --- |
| `"disallow-in-func"` | Also report `setState` in a function inside `componentDidMount`. |

{/* bad {"options": ["disallow-in-func"]} */}
```jsx
class Profile extends React.Component {
  componentDidMount() {
    loadUser(this.props.id).then(user => {
      this.setState({ user });
    });
  }
}
```

## When not to use it

Measuring the DOM needs this pattern. For example, a tooltip must render once before you can read its size and store the position. React flushes that second render before the browser paints.