react/no-did-mount-set-state

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.

Configure

Off by default. To turn it on:

[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.

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

Examples

Reported:

class Profile extends React.Component {
  componentDidMount() {
    this.setState({ name: this.props.name.toUpperCase() });
  }
}

Not reported:

class Profile extends React.Component {
  state = { name: this.props.name.toUpperCase() };

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

Options

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.