React - Functional error boundaries

_readme.md

React - Functional error boundaries

Thanks to React hooks you have now happily turned all your classes into functional components.

Wait, all your components? Not quite. There is one thing that can still only be implemented using classes: Error boundaries.

There is just no functional equivalent for componentDidCatch and deriveStateFromError yet.

Proposed solution

The proposed solution is greatly inspired by the new React.memo() API.

import Catch from "./functional-error-boundary"

type Props = {
  children: React.ReactNode
}

const MyErrorBoundary = Catch(function MyErrorBoundary(props: Props, error?: Error) {
  if (error) {
    return (
      <div className="error-screen">
        <h2>An error has occured</h2>
        <h4>{error.message}</h4>
      </div>
    )
  } else {
    return <React.Fragment>{props.children}</React.Fragment>
  }
})

API

type ErrorHandler = (error: Error, info: React.ErrorInfo) => void

Catch(component: React.ComponentType)

Catch(component: React.ComponentType, errorHandler: ErrorHandler)

Wraps the functional component component to make it an error boundary. The caught error is passed to the component function as a second parameter.

The optional second argument to Catch() (errorHandler) is a function that acts as componentDidCatch(). Use it to handle side effects like error logging.

Implementation

Find the code below.

Outlook

Would be great to see something like this integrated into the React.js core library:

import React from "react"

type Props = {
  children: React.ReactNode
}

const MyErrorBoundary = React.Catch(function MyErrorBoundary(props: Props, error?: Error) {
  if (error) {
    return (
      <div className="error-screen">
        <h2>An error has occured</h2>
        <h4>{error.message}</h4>
      </div>
    )
  } else {
    return <React.Fragment>{props.children}</React.Fragment>
  }
})

functional-error-boundary.tsx

import React from "react"

type ErrorHandler = (error: Error, info: React.ErrorInfo) => void
type ErrorHandlingComponent<Props> = (props: Props, error?: Error) => React.ReactNode

type ErrorState = { error?: Error }

export default function Catch<Props extends {}>(
  component: ErrorHandlingComponent<Props>,
  errorHandler?: ErrorHandler
): React.ComponentType<Props> {
  return class extends React.Component<Props, ErrorState> {
    state: ErrorState = {
      error: undefined
    }
    
    static getDerivedStateFromError(error: Error) {
      return { error }
    }
    
    componentDidCatch(error: Error, info: React.ErrorInfo) {
      if (errorHandler) {
        errorHandler(error, info)
      }
    }
    
    render() {
      return component(this.props, this.state.error)
    }
  }
}

Yeah, I guess there's only so many ways to write such a component and stick to existing API patterns 🙂

🙂

I really see no point in exporting a function when ultimately all I'll be doing will be cloaking a class instance inside a function. Why not just use the class directly? Wouldn't hurt to have a single class component rather than going through all this complexity, don't you think?

I really see no point in exporting a function when ultimately all I'll be doing will be cloaking a class instance inside a function. Why not just use the class directly? Wouldn't hurt to have a single class component rather than going through all this complexity, don't you think?

Absolutely. I can't see the issue here with just using the class component for ErrorBoundary.

@andywer Could you please show an example of how we can use it?

@manakupadhyay It can be used as in the example at the top, under "Outlook", just that it's not part of React:

type Props = {
  children: React.ReactNode
}

const MyErrorBoundary = Catch(function MyErrorBoundary(props: Props, error?: Error) {
  if (error) {
    return (
      <div className="error-screen">
        <h2>An error has occured</h2>
        <h4>{error.message}</h4>
      </div>
    )
  } else {
    return <React.Fragment>{props.children}</React.Fragment>
  }
})

and then

function MyComponent() {
  return (
    <MyErrorBoundary>
      <ContentThatMightThrow>
    </MyErrorBoundary>
  );
}

@andywer Thanks a lot :)

Well I am not a fan of functional components and stick to class based components but Thanks anyway for writing this.

i tried it works great how but it should reset the state of error if click on something and it takes me to a new route how can i do that i tried to see where can i do it but couldnt find any appropriate place