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Day 22: A sensible default

Our withPokemon HOC is mostly reusable. But it displays that static loading... message.

Let’s make that replaceable.

Components over configuration

The defaultProps API is one of my favorites. Use it to provide sensible defaults for your components.

For withPokemon, we should always indicate that the component is doing work. But we should make make the message configurable.

We know that props can be components. So lets put <div>loading...</div> in defaultProps.

class FetchPokemon extends React.Component { ... }

FetchPokemon.defaultProps = {
  renderLoading: <div>loading...</div>
}

(Yes, this works with component functions and classes alike.)

Now we update render() and anyone on the team can use any loading component they want.

return this.state.character ? (
  <Component character={this.state.character} />
) : (
  this.props.renderLoading
)

Future syntax

CodeSandbox and create-react-app provide syntactic sugar for defaultProps.

class FetchPokemon extends React.Component {
  static defaultProps = {
    renderLoading: <div>loading...</div>,
  }
}

It reduces redundant typing but only for class components.

Tinker with it

Use the workspace below and explore defaultProps.

  • Change static defaultProps to today’s syntax and back again.
  • Change renderLoading to use a render prop. What changes in render()?
  • Create a new functional component named Loading and use it in defaultProps. What changes in render()?
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