Conditional Rendering in React

In React apps, you’ll often need to render different UI components conditionally based on certain state. For example, showing a login form if a user is not authenticated, or displaying different content based on configurable settings.

Here are useful patterns for conditional rendering in React:

If/Else Statements

The standard JS if/else statement works in JSX too:

function App() {
  const loggedIn = false;
  
  if (loggedIn) {
    return <WelcomeMessage />;
  } else {
    return <LoginForm />;
  }
}

This will render either the WelcomeMessage or LoginForm component based on the value of loggedIn.

Ternary Operator

function App() {
  const isLoading = true;

  return (
    <div>
      {isLoading ? <Loader /> : <Content />} 
    </div>
  )
}

If isLoading is truthy, it will render the Loader, else render Content.

Short Circuit Evaluation

You can take advantage of JS short circuit evaluation:

function App() {
  const showAlert = false;
  
  return (
    <div>
      {showAlert && <Alert />}
    </div>
  )
}

If showAlert is falsy, React won’t even evaluate the <Alert /> expression.

Element Variables

You can store elements in variables for conditional rendering:

function App() {
  let message;
  if (user) {
    message = <WelcomeMessage />;
  } else {
    message = <SignUpMessage />;
  }

  return <div>{message}</div>;
}

Preventing Component Rendering

For more control, you can return null to prevent rendering:

function App(props) {
  if (!props.authorized) {
    return null;
  }

  return <AdminPanel />;
}

By returning null, App won’t render anything if props.authorized is falsy.

Showing/Hiding Elements

Another option is conditionally applying the hidden attribute:

return (
  <div>
    <Alert hidden={!error} /> 
  </div>
)

The Alert will be hidden if error is falsy.

Conclusion

There are a few different ways to conditionally render in React:

• If/else statements
• Ternary expressions
• Short circuit evaluation
• Returning null or using hidden attributes

Choose the right method based on your use case. Conditional rendering is essential for building reusable React components that adapt to different states.