The key to achieving infinite scrolling is to listen to scroll events and trigger loading. The core steps include: 1. By listening to scroll events and calculating the scroll position, judging whether the bottom is reached; 2. Use throttling and locking mechanisms to prevent duplicate requests; 3. After loading the data, update the DOM and page height and handle the boundary situation; 4. Optionally use Intersection Observer to improve performance. The specific method is to use JavaScript to monitor the scroll position, load new content when it is close to the bottom, add buffers to avoid blanks, and set the isLoading flag and throttle to control the request frequency. After the data is loaded, update the container height and check whether there is more data. You can also add loading animation optimization experience. For more efficient implementations, you can use the Intersection Observer API to replace scroll listening.

It is actually not difficult to achieve infinite scrolling, but to make the experience smooth and the performance stable, you need to pay attention to some key points. The core idea is: when the user scrolls to the bottom of the page, new content is automatically loaded , rather than relying on the page turn button.

Listen to scroll events and determine whether they are bottoming out

To achieve infinite scrolling, the first step is to monitor the user's scrolling behavior and determine whether it is about to roll to the bottom. A common practice is to use JavaScript's window.addEventListener('scroll', ...) to listen for scrolling positions.

To determine whether it is close to the bottom, you can use the following formula:

 const scrollTop = window.scrollY || document.documentElement.scrollTop;
const windowHeight = window.innerHeight;
const bodyHeight = document.body.scrollHeight;

if (scrollTop windowHeight >= bodyHeight - 500) {
  // Load more data}

A 500px "buffer" is added here to load it in advance to avoid users seeing blank spaces.

• The buffer value can be adjusted according to the network speed and content size (for example, set to 1000 under the slow network)
• It is not recommended to be too small, otherwise you may not have time to load and roll to the end
• If the page has a fixed footer, also consider its height

Prevent duplicate requests and throttling control

A common problem is that when a user scrolls quickly, the loading function may be triggered multiple times, causing requests to pile up. To avoid this problem, two things need to be done:

• Throttling : Limits the execution frequency of scroll events, such as execution every 300ms.
• Loading lock : Set a flag during data loading to prevent repeated requests.

The sample code is as follows:

 let isLoading = false;

function loadMoreData() {
  if (isLoading) return;
  isLoading = true;

  fetch('/api/data')
    .then(res => res.json())
    .then(data => {
      // Insert new data isLoading = false;
    });
}

window.addEventListener('scroll', throttle(loadMoreData, 300));

You can also use Lodash's _.throttle or write a simple throttling function yourself.

Updates and boundary judgments after data loading are completed

After loading the data, in addition to inserting the content into the DOM, there are a few details to pay attention to:

• After inserting new content, remember to update the total height of the page, otherwise the next judgment will be inaccurate.
• Determine if there is more data, if not, no loading logic will be bound or the "No more" prompt will be displayed
• Optionally add a loading animation to improve user experience

For example:

 function appendData(data) {
  const container = document.getElementById('content');
  data.forEach(item => {
    const div = document.createElement('div');
    div.textContent = item.title;
    container.appendChild(div);
  });

  if (data.length === 0) {
    console.log('No more content');
    window.removeEventListener('scroll', loadMoreData);
  }
}

Using Intersection Observer is a better choice (optional)

Using the Intersection Observer API is more efficient than directly listening to scroll events, especially in complex pages.

You can create an "observer" that monitors whether a "trigger element" enters the visual area and starts loading data once it enters.

Basic usage:

 const observer = new IntersectionObserver(entries => {
  if (entries[0].isIntersecting) {
    loadMoreData();
  }
});

observer.observe(document.getElementById('infinite-trigger'));

This reduces dependence on scroll events and improves performance.

Basically that's it.
Unlimited scrolling seems simple, but it is not easy to do a good job of experience and performance optimization. As long as you pay attention to the trigger conditions, anti-shake throttling, and loading state control, you can achieve a relatively stable implementation.

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