@modular-component/with-default-props

Provides a with(defaultProps) stage allowing to set default value for props. Contrary to the standard React defaultProps field, the with(defaultProps) stage can also set new props that are not surfaced by the component, and react to passed props (or other previous stages) to dynamically compute a default value.

Usage

import { ModularComponent } from '@modular-component/core'
import { defaultProps } from '@modular-component/with-default-props'

const MyComponent = ModularComponent<{ someFlag?: boolean }>()
  .with(defaultProps({
    someFlag: false,
    someNewProp: 'hello world'
  }))
  .with(render(({ props }) => (
    // props is inferred as { someFlag: boolean; someNewProp: string } at this point
  )))

const MyDynamicProps = ModularComponent<{ 
  role: 'user' | 'owner' | 'admin', 
  canEdit?: boolean, 
  canDelete?: boolean 
}>()
  .with(defaultProps(({ props }) => ({
    canEdit: ['owner', 'admin'].includes(props.role),
    canDelete: ['owner'].includes(props.role)
  }))
  .with(render(({ props }) => {
    // props is inferred as { role: 'user' | 'owner' | 'admin'; canEdit: boolean; canDelete: boolean }
    // canEdit defaults to true if the role is not "user", false otherwise
    // canDelete defaults to true if the role is "admin", false otherwise
    // canEdit and canDelete can still be controlled by explicitely setting the property
  })))

Implementation

with(defaultProps) runs a custom stage hook to shallowly merge the default props to the received component props. Accepted values are restricted to a partial map of the original props to only accept correct types for defined props. The value can also be a function of the current args.

import { ModularStage } from '@modular-component/core'

type Merge<Props, DefaultProps extends Partial<Props>> = {
  [key in keyof Props | keyof DefaultProps]-?: key extends keyof Props
    ? key extends keyof DefaultProps
      ? NonNullable<Props[key]>
      : Props[key]
    : DefaultProps[key]
}

export function defaultProps<
  Args extends { props: {} },
  Props extends Args extends { props: infer U } ? U : {},
  DefaultProps extends Partial<Props>,
>(
  defaultProps: DefaultProps | ((args: Args) => DefaultProps),
): ModularStage<
  'props',
  (args: Args) => Merge<Props, DefaultProps>
> {
  return {
    field: 'props',
    useStage: (args: Args) =>
      ({
        ...(typeof defaultProps === 'function' ? defaultProps(args) : defaultProps),
        ...args.props,
      } as Merge<Props, DefaultProps>),
  }
}