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React Tips

React Tips and Tricks — Fragments and Error Handling

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React is the most used front end library for building modern, interactive front end web apps. It can also be used to build mobile apps. In this article, we’ll look at some tips and tricks to make building apps with React easier.

React Fragments

We can’t have multiple root nodes in a React component. However, we can have a single root node that doesn’t render any component by using a React fragment as the root node.

We can reference a React fragment with the React.Fragement component or an empty tag.

For instance, we can write the following:

import React from "react";
`
export default function App() {
  return (
    <React.Fragment>
      <p>foo</p>
      <p>bar</p>
    </React.Fragment>
  );
}

or:

import React from "react";
`
export default function App() {
  return (
    <>
      <p>foo</p>
      <p>bar</p>
    </>
  );
}

<React.Fragment> is the same as <> .

Use Error Boundaries to Handle Errors Gracefully

Error boundaries are components that are displayed when there’re errors. They have special hooks like componentDidCatch to let us retrieve error details and does actions on error accordingly.

We wrap error boundary components around components that may throw errors for them to work.

Error boundary components are always class-based components. There’s no function component equivalent for this.

For instance, we can define an error boundary component and use it as follows:

import React from "react";
`
function Foo() {
  throw new Error("error");
  return <div>foo</div>;
}
`
class ErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }
  componentDidCatch(error, info) {
    this.setState({ hasError: true });
  }
  render() {
    if (this.state.hasError) {
      return <h1>Error occurred.</h1>;
    }
    return this.props.children;
  }
}
`
export default function App() {
  return (
    <ErrorBoundary>
      <Foo />
    </ErrorBoundary>
  );
}

In the code above, we defined the ErrorBoundary component, which has the componentDidCatch hook, which takes the error parameter with the error that’s raised, and info object with the error information.

Then we call setState to hasError to true so that we render an error message. We return this.props.children when there’re no errors so that we display the components that we put inside the ErrorBoundary component.

Therefore, when we have Foo , where we threw an error, then we display the ‘Error occurred’ message since Foo throws an error before rendering anything.

Higher-Order Components

Higher-order components are components that render other components. It’s useful because it can be used to produce components that are modified by the higher-order component.

For instance, we can create a colorizeElement higher-order component to apply the color prop to a component with the value blue as the default. If the color prop is set, then it’ll override the value of the color prop that we pass inside.

We can create and use it as follows:

import React from "react";
`
const colorizeElement = Element => props => <Element color="blue" {...props} />;
`
const Foo = ({ color }) => {
  return <p style={{ color }}>foo</p>;
};
`
const ColoredFoo = colorizeElement(Foo);
`
export default function App() {
  return (
    <>
      <ColoredFoo color="red" />
      <ColoredFoo />
    </>
  );
}

In the code above, we have the ColoredFoo component that we created from the colorizeElement higher-order component. In the component, we pass in the Element , which is a React component, which returns a new function with props as a parameter and returns the Element with the color prop set as 'blue' and also pass in other props that are passed in.

Then in App , we have the ColoredFoo components, one with color prop set and the other one without. Then the first one is red and the second is blue.

React DevTools

React dev tools is an extension for Chrome and Firefox and it’s maintained by the React core team. It lets us inspect the values of props and states that are inside components.

We’ll run into bugs and issues that are hard to solve eventually, so it’s a handy tool for debugging.

Conclusion

Error boundaries and higher-order components are great for displaying errors and modifying components respectively.

Fragments are great for rendering multiple items within one single root node. It doesn’t render any HTML element itself.

React dev tools is a great extension for debugging.

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