Loading states for data in NextJS - Deep Dive

Overview - Loading states for data

What is it?

Loading states for data are visual or logical indicators that show users when data is being fetched or processed in a Next.js application. They help communicate that the app is working on getting information, so users know to wait instead of thinking the app is broken. These states can be simple text messages, spinners, or skeleton screens that appear while data loads.

Why it matters

Without loading states, users might see blank screens or stale content and think the app is slow or broken. This causes frustration and can make users leave. Loading states improve user experience by giving clear feedback, making apps feel faster and more reliable. They also help developers handle asynchronous data fetching smoothly.

Where it fits

Before learning loading states, you should understand React components and basic data fetching in Next.js. After mastering loading states, you can explore advanced data fetching strategies like server-side rendering, incremental static regeneration, and React Suspense for data fetching.

Mental Model

Core Idea

Loading states are temporary signals that tell users data is on its way, preventing confusion and improving experience.

Think of it like...

It's like waiting in line at a coffee shop: a barista might show you a progress light or call your name so you know your order is being prepared, instead of wondering if they forgot you.

┌───────────────┐
│ User requests │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Loading state │  <-- Shows spinner or message
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Data received │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Render content│
└───────────────┘

Build-Up - 6 Steps

1

Foundation

What is a loading state?

Concept: Introduce the idea that apps need to show something while waiting for data.

When a Next.js app asks a server for data, it takes time to get the answer. During this time, the app can show a loading state like a spinner or message so users know it's working. Without it, users might see nothing or old data and get confused.

Result

Users see a clear indication that data is loading instead of a blank or frozen screen.

Understanding loading states is the first step to making apps feel responsive and trustworthy.

2

Foundation

Basic loading state with useState

Concept: Show how to use React's useState to track loading and display a message.

In a Next.js component, you can use useState to create a loading flag. When you start fetching data, set loading to true. When data arrives, set loading to false. Render a message or spinner when loading is true, and show data when false.

Result

The component shows 'Loading...' text while waiting, then displays the data.

Using state to track loading is simple but powerful for controlling what users see.

3

Intermediate

Loading states with async data fetching

🤔Before reading on: do you think loading states should be set before or after the fetch call? Commit to your answer.

Concept: Learn to set loading states correctly around asynchronous fetch calls.

When fetching data with async/await, set loading to true before the fetch starts. Await the fetch call, then set loading to false after data arrives. This ensures the loading state covers the entire waiting period.

Result

Loading indicator appears exactly while data is being fetched, then disappears when done.

Knowing when to toggle loading state prevents flickers or missing feedback during data fetch.

4

Intermediate

Using Next.js built-in loading UI with Suspense

🤔Before reading on: do you think React Suspense works for all data fetching in Next.js by default? Commit to yes or no.

Concept: Explore React Suspense to handle loading states declaratively in Next.js.

React Suspense lets you wrap components that fetch data and show a fallback UI while waiting. Next.js supports Suspense for server components and client components with data fetching libraries. You wrap your data component in }>, and React shows the fallback automatically.

Result

Loading UI appears automatically without manual state management during data fetch.

Suspense simplifies loading states by letting React handle when to show loading UI.

5

Advanced

Skeleton screens for perceived performance

🤔Before reading on: do you think showing a blank spinner or a skeleton screen feels faster to users? Commit to your answer.

Concept: Learn how skeleton screens improve user perception of speed during loading.

Instead of a spinner, skeleton screens show a gray placeholder shaped like the content. This gives users a sense of structure and progress. In Next.js, you can render skeleton components during loading states to mimic the layout of the final content.

Result

Users feel the app is faster and more polished because they see a preview of content shape.

Using skeleton screens taps into human perception to reduce frustration during waits.

6

Expert

Handling loading states with Next.js App Router and server components

🤔Before reading on: do you think loading states are needed for server components that fetch data on the server? Commit to yes or no.

Concept: Understand how Next.js App Router uses special loading.js files and server components for loading states.

In Next.js 13+, server components fetch data on the server before sending HTML. You can create a loading.js file in a route folder to show a loading UI while the server prepares the page. This separates loading UI from client logic and improves performance and user experience.

Result

Loading UI appears automatically during server-side data fetching without client-side state management.

Knowing Next.js App Router loading conventions helps build fast, user-friendly apps with minimal client code.

Under the Hood

Loading states work by tracking the asynchronous process of data fetching. When a fetch starts, a loading flag is set to true, triggering the UI to show a loading indicator. Once data arrives, the flag switches to false, and the UI updates to show the data. In Next.js, server components fetch data before rendering HTML, so loading states can be handled on the server or client depending on the component type. React Suspense uses a special mechanism to pause rendering and show fallback UI until data is ready.

Why designed this way?

Loading states were designed to solve the problem of uncertain wait times in web apps. Early web pages were static, so users never waited for data. Modern apps fetch data dynamically, so users need feedback to avoid confusion. React Suspense and Next.js server components were created to simplify loading state management by integrating it into the rendering lifecycle, reducing manual state handling and improving performance.

┌───────────────┐
│ Start fetch   │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Set loading = │
│ true         │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Fetch data    │
│ (async)      │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Data received │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Set loading = │
│ false        │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Render data   │
└───────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do loading states only matter for slow internet connections? Commit to yes or no.

Common Belief: Loading states are only needed when the internet is slow or the server is slow.

Reality: Loading states improve user experience even on fast connections by providing clear feedback and preventing flickers or confusion.

Why it matters: Without loading states, users might think the app is broken or frozen, even if data loads quickly.

Quick: Do you think React Suspense automatically works with all data fetching methods? Commit to yes or no.

Common Belief: React Suspense works out of the box with any data fetching in Next.js.

Reality: Suspense requires special data fetching libraries or server components that support it; it doesn't work automatically with plain fetch calls.

Why it matters: Assuming Suspense works everywhere can lead to bugs or missing loading UI.

Quick: Do you think showing a spinner is always better than a skeleton screen? Commit to yes or no.

Common Belief: A spinner is the best way to show loading because it clearly indicates waiting.

Reality: Skeleton screens often feel faster and less frustrating because they show the shape of content, reducing perceived wait time.

Why it matters: Choosing the wrong loading UI can hurt user experience and make apps feel slower.

Quick: Do you think server components never need loading states? Commit to yes or no.

Common Belief: Server components fetch data before rendering, so loading states are unnecessary.

Reality: Server components can still benefit from loading UI during navigation or slow server responses, handled via loading.js files in Next.js App Router.

Why it matters: Ignoring loading states in server components can cause blank screens or jarring transitions.

Expert Zone

1

Loading states can be nested and combined with error states to create robust user feedback flows.

2

Using React Suspense with data fetching libraries like React Query or SWR requires understanding their suspense modes and cache behaviors.

3

Next.js App Router's loading.js files allow granular control of loading UI per route segment, enabling progressive loading experiences.

When NOT to use

Avoid manual loading states when using Next.js server components with loading.js files or React Suspense-enabled data fetching libraries, as these handle loading UI automatically. Instead, rely on these built-in mechanisms for cleaner code and better performance.

Production Patterns

In production, developers use skeleton screens for main content areas, spinners for small widgets, and Next.js loading.js files for route-level loading. They combine Suspense with data fetching libraries to minimize boilerplate and improve user experience. Progressive loading with nested loading states is common in complex apps.

Connections

User Experience Design

Loading states are a key part of UX design patterns for feedback and perceived performance.

Understanding loading states helps designers create interfaces that keep users informed and reduce frustration during waits.

Asynchronous Programming

Loading states directly relate to managing asynchronous operations and their lifecycle.

Knowing how async code works clarifies when and how to show loading indicators effectively.

Traffic Control Systems

Loading states act like traffic signals that manage user expectations and flow.

Just as traffic lights prevent chaos by signaling when to stop or go, loading states prevent confusion by signaling when data is ready.

Common Pitfalls

#1 Showing data before it is fully loaded causes flickering or errors.

Wrong approach:

const [loading, setLoading] = useState(false);
useEffect(() => {
fetchData().then(data => {
setData(data);
});
}, []);
return loading ? : ;

Correct approach:

const [loading, setLoading] = useState(true);
useEffect(() => {
fetchData().then(data => {
setData(data);
setLoading(false);
});
}, []);
return loading ? : ;

Root cause:

Not setting loading to true before fetch causes the UI to skip the loading state.

#2 Using a spinner for all loading states makes the app feel slow and boring.

Wrong approach:

return loading ? : ;

Correct approach:

return loading ? : ;

Root cause:

Ignoring perceived performance and user psychology leads to poor loading UI choices.

#3 Not handling loading states in nested components causes inconsistent UI feedback.

Wrong approach:

Parent shows loading, but child fetches data without loading state, causing blank areas.

Correct approach:

Both parent and child components manage their own loading states or use Suspense boundaries.

Root cause:

Assuming one loading state covers all nested data fetches leads to UI gaps.

Key Takeaways

Loading states are essential to communicate data fetching progress and keep users informed.

Managing loading states properly requires understanding asynchronous data flow and React state.

React Suspense and Next.js App Router loading.js files provide modern, declarative ways to handle loading UI.

Skeleton screens improve perceived performance better than simple spinners by showing content structure.

Ignoring loading states or handling them poorly leads to confusing, frustrating user experiences.