prefer-exact-props.md

Prefer exact proptype definitions (react/prefer-exact-props)

Recommends options to ensure only exact prop definitions are used when writing components. This recommends solutions for PropTypes or for Flow types.

In React, you can define prop types for components using propTypes. Such an example is below:

class Foo extends React.Component {
  render() {
    return <p>{this.props.bar}</p>;
  }
}

Foo.propTypes = {
  bar: PropTypes.string
};

The problem with this is that the consumer of the component could still pass in extra props. There could even be a typo for expected props. In order to prevent those situations, one could use the npm package prop-types-exact to warn when unexpected props are passed to the component.

One can also define props for a component using Flow types. Such an example is below:

class Foo extends React.Component {
  props: {
    bar: string
  }

  render() {
    return <p>{this.props.bar}</p>;
  }
}

In this case, one could instead enforce only the exact props being used by using exact type objects, like below:

class Foo extends React.Component {
  props: {|
    bar: string
  }|

  render() {
    return <p>{this.props.bar}</p>;
  }
}

See the Flow docs on exact object types for more information.

Rule Details

This rule will only produce errors for prop types when combined with the appropriate entries in propWrapperFunctions. For example:

{
  "settings": {
    "propWrapperFunctions": [
      {"property": "exact", "exact": true}
    ]
  }
}

The following patterns are considered warnings:

  class Component extends React.Component {
    render() {
      return <div />;
    }
  }
  Component.propTypes = {
    foo: PropTypes.string
  };

  class Component extends React.Component {
    static propTypes = {
      foo: PropTypes.string
    }
    render() {
      return <div />;
    }
  }

  class Component extends React.Component {
    props: {
      foo: string
    }
    render() {
      return <div />;
    }
  }

  function Component(props: { foo: string }) {
    return <div />;
  }

  type Props = {
    foo: string
  }
  function Component(props: Props) {
    return <div />;
  }

The following patterns are not considered warnings:

  type Props = {|
    foo: string
  |}
  function Component(props: Props) {
    return <div />;
  }

  import exact from 'prop-types-exact';
  class Component extends React.Component {
    render() {
      return <div />;
    }
  }
  Component.propTypes = exact({
    foo: PropTypes.string
  });

When Not To Use It

If you aren't concerned about extra props being passed to a component or potential spelling errors for existing props aren't a common nuisance, then you can leave this rule off.