Web Workers are suitable for handling time-consuming tasks to avoid blocking the main thread. The steps to create a Web Worker include: 1. Prepare the worker.js file; 2. Create an instance through new Worker() in the main thread; 3. Use postMessage() to send messages; 4. Receive results through onmessage; 5. Calling terminate() to terminate when not in use. Suitable tasks include a large number of mathematical operations, timing tasks, data preloading and processing, and long-running tasks. Notes include: communication overhead is high, Transferable Objects should be used; DOM and some global variables cannot be accessed; debugging is more troublesome; multiple workers should not be abused.
Web Workers in H5 (HTML5) are a very practical function, especially suitable for handling some time-consuming background tasks on web pages, such as data calculation, file parsing, timing tasks, etc. It can effectively prevent these tasks from blocking the main thread, thereby improving page response speed and user experience.
The following is a few common usage scenarios and talk about the actual usage and precautions of Web Workers.
How to create and start a Web Worker
Web Worker is a standalone thread created through JavaScript. Its core is to run a script in an environment isolated from the main thread.
The basic steps are as follows:
- Prepare a separate JS file, such as
worker.js, which writes the code you want to execute in the background. - Create a worker instance in the main page using
new Worker('worker.js'). - Use
postMessage()to send a message to the worker. - The worker can also return the result through
postMessage(). - If you don't need it, you can call
worker.terminate()to terminate.
For example: you can send a number in the main thread, and the worker calculates its squared and returns.
// Main thread const worker = new Worker('worker.js');
worker.postMessage(10);
worker.onmessage = function(e) {
console.log('Result received:', e.data); // Output 100
} // worker.js
onmessage = function(e) {
const result = e.data * e.data;
postMessage(result);
}Which tasks are suitable for handling by Web Worker
Not all tasks are suitable for worker, but the following situations are suitable:
- A large number of mathematical operations : such as image processing, encryption and decryption, compression/decompression, etc.
- Timing tasks : Even if page switching or user operations are frequent, the timing logic can be ensured that the timing logic is not interrupted.
- Data preloading and processing : For example, after obtaining the original data from the interface, format conversion, filtering, aggregation and other operations are performed in the worker.
- Long-running tasks : such as WebSocket long connection monitoring, heartbeat detection, etc.
It should be noted that the worker does not have DOM operation permissions and cannot directly update the page content. If you need to update the UI, you must send the result back to the main thread through the message mechanism.
FAQs and optimization suggestions in use of Web Worker
Although Web Worker is powerful, there are some details that are easy to ignore during use:
- Communication overhead cannot be ignored : data transfer between the worker and the main thread is a "copy" process. If the data passed is large, it will affect performance. Consider using
Transferable Objects(such asArrayBuffer) to reduce copy costs. - Some global variables cannot be accessed : such as
windowanddocument, and only some APIs can be used, such assetTimeout,fetch, etc. - Debugging is relatively troublesome : The browser developer tools support worker is already good, but it is still not as convenient as the main thread. It is recommended to add log output or encapsulate debugging functions.
- Don't abuse multiple workers : Each worker is a thread, and more threads will increase the system burden. Reasonably control the number and reuse existing workers if necessary.
Basically that's it. Web Worker is not complex, but it can significantly improve application performance in many scenarios, especially when dealing with data-intensive tasks. As long as you pay attention to inter-thread communication and resource management, it can play its role well.
The above is the detailed content of H5 Web Workers for Background Data Processing. For more information, please follow other related articles on the PHP Chinese website!
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