The SuspenseList component in React is a relatively new addition that is part of the React Suspense feature set. It is designed to control the order in which multiple suspended components (components that are waiting for asynchronous operations to complete, like data fetching or lazy loading) are rendered. This allows for more control over how the loading states of those components are displayed in a more predictable and efficient way.

Purpose of SuspenseList:

• Concurrent Rendering: When working with concurrent React features (like React.lazy or Suspense), you may have several components that are suspended (waiting for some asynchronous operation like data fetching or code splitting). The SuspenseList component helps manage the rendering sequence of these suspended components.
• Control the order of appearance: By using SuspenseList, you can control whether you want the suspended components to appear in the order they were rendered or in a specific order, and even delay showing components until others are ready.

Features of SuspenseList:

• Reveal Order: You can control how suspended components are revealed by specifying a revealOrder prop. This prop can help you choose whether to render components in the order they were rendered or one by one, depending on your design choice.
• Fallback Content: Like the standard Suspense component, SuspenseList also allows you to define a fallback UI that will be displayed while components are waiting for their data.

SuspenseList Props:

• revealOrder: Determines how the suspended components are revealed. It can be one of:

  • 'forwards': Suspended components are revealed in the order they were rendered.
  • 'backwards': Suspended components are revealed in reverse order.
  • 'together': All suspended components are revealed simultaneously once all are ready.

• tail: A fallback UI that will be shown when the components in the list are still suspended. You can use this for a custom loading experience, or even a spinner, to show while the components are still loading.

Example of Using SuspenseList:

import React, { Suspense, lazy } from 'react';

// Lazy load components
const ComponentA = lazy(() => import('./ComponentA'));
const ComponentB = lazy(() => import('./ComponentB'));
const ComponentC = lazy(() => import('./ComponentC'));

function App() {
return (
<SuspenseList revealOrder="forwards" tail={<div>Loading components...</div>}>
<Suspense fallback={<div>Loading Component A...</div>}>
<ComponentA />
</Suspense>
<Suspense fallback={<div>Loading Component B...</div>}>
<ComponentB />
</Suspense>
<Suspense fallback={<div>Loading Component C...</div>}>
<ComponentC />
</Suspense>
</SuspenseList>
);
}

export default App;

1. Lazy Loading: ComponentA, ComponentB, and ComponentC are loaded lazily using React.lazy().
2. Suspense: Each component is wrapped in a Suspense component, with a fallback UI provided for each.
3. SuspenseList: The SuspenseList component is used to control the order in which the components are rendered when they are ready. The revealOrder="forwards" prop ensures that they are revealed in the order they were originally rendered.

How It Works:

• Without SuspenseList: If you use Suspense directly for each component, each component will be rendered independently. However, if one component takes longer to load than the others, the user might see those components render at different times.

• With SuspenseList: It helps you control the order of component rendering more precisely. For example, if you want all components to render together only after all are ready, you can set revealOrder="together".

When to Use SuspenseList:

• You have multiple asynchronous components (e.g., lazy-loaded components or data-fetching components) that you want to load in a specific sequence or display in a controlled manner.
• You want to fine-tune the UX, ensuring that components render in the right order for a more cohesive experience.

Benefits of SuspenseList:

• It provides a way to control the loading sequence of multiple suspended components.
• It can improve the user experience by giving more predictable and smoother loading behaviors.
• It makes it easier to handle complex loading states when multiple components are suspended.

In summary, SuspenseList is a useful tool for managing the rendering order of multiple suspended components in React, especially when you’re working with concurrent features like React.lazy and Suspense.