The core way to not let the browser get stuck when processing large amounts of data is to avoid blocking the main thread. Specific practices include: 1. Use requestIdleCallback or setTimeout to slice the task and perform it step by step to free up CPU time; 2. Use Web Worker to process complex calculations in independent threads to avoid affecting the main thread; 3. Use virtual scrolling technology to render only the list items of the visual area to reduce the DOM burden; 4. Combining data preprocessing and lazy loading, loading data on demand to reduce the initial pressure. These strategies can effectively keep the interface smooth and improve the user experience.

The key to avoid blocking the main thread when processing large amounts of data is to avoid blocking the main thread. The browser's JavaScript is run by a single thread. Once the time-consuming operation is performed (such as traversing hundreds of thousands of data), the page will lose its response. The core idea of ??solving this problem is: break down heavy tasks, execute them asynchronously, or hand them over to background threads for processing .

Below are some practical methods and techniques that can effectively improve the user experience while keeping the interface smooth.

1. Use requestIdleCallback or setTimeout to handle sharding

If you have to process data on the main thread, you can split the task into small pieces and perform step by step when the browser is idle. This allows CPU time to render for the UI.

• requestIdleCallback : Suitable for low priority tasks, but with average compatibility.
• setTimeout(fn, 0) or setInterval : More general and suitable for most scenarios.

For example:

 function processChunk(data, index = 0, chunkSize = 1000) {
  const end = Math.min(index chunkSize, data.length);
  for (let i = index; i < end; i ) {
    // Process each piece of data}

  if (end < data.length) {
    setTimeout(() => processChunk(data, end, chunkSize), 0);
  }
}

This will only process a portion of the data at a time, giving the browser the opportunity to render the UI and respond to user operations.

2. Use Web Worker to handle complex computing

Web Worker can run scripts in standalone threads without affecting the main thread at all. This is the most recommended way to parse JSON, sort, filter and other heavy tasks.

How to use it is roughly as follows:

1. Create a worker file (such as worker.js ):

    onmessage = function(e) {
     const result = heavyProcessing(e.data);
     postMessage(result);
   };

2. Call it in the main thread:

    const worker = new Worker('worker.js');
   worker.onmessage = function(e) {
     console.log('processing result:', e.data);
   };
   worker.postMessage(largeData);

   Note: DOM cannot be accessed in Worker, and certain browser APIs (such as document , alert , etc.) cannot be used.

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   3. Virtual Scrolling rendering list

   If the problem is to showcase big data rather than dealing with the data itself, virtual scrolling is a good solution. It renders only elements within the visual area, greatly reducing the number of DOM nodes.

   Common practices:

   • Calculate the height and scroll position of the current visual area
   • Render only the data items in the "visible" part
   • Dynamically update rendered content, changing with scrolling

   You can implement a simple virtual scrolling logic yourself, or use ready-made libraries such as react-virtual or Vue's vue-virtual-scroller .

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   4. Combining data preprocessing and lazy loading

   Sometimes, we don't actually need to load all the data from the beginning. You can first load a part and get more as needed when the user scrolls to the bottom or switches page numbers.

   for example:

   • Front-end gets data from interface pagination
   • Pull 50~100 pieces each time instead of pulling tens of thousands at a time
   • Improve the experience with the skeleton screen or loading animation

   This strategy not only reduces front-end pressure, but also reduces back-end bandwidth consumption.

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   Basically these common methods are. Which one to choose depends on your specific needs: if it is just a rendering problem, virtual scrolling is the most suitable; if it is a problem, sharding or Web Worker is the most suitable. The core principle is: not occupying the main thread for a long time .

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