Web Worker is a multi-threaded solution provided by HTML5, allowing JavaScript to run in background threads to avoid blocking the main thread. It improves page response speed by executing time-consuming tasks such as data calculations, network requests, etc. through independent threads. 1. Worker cannot operate DOM or use window/document objects; 2. Use postMessage and onmessage to achieve main thread communication; 3. It is suitable for complex computing, timing tasks, parallel processing and other scenarios; 4. Notes include not loading scripts across domains, not being able to use synchronization methods such as alert, and message delivery is restricted by structured cloning. Rational use of Web Worker can significantly optimize performance bottlenecks.

Web Workers is a technology used to run JavaScript in HTML5 in background threads. That is to say, it allows your web page to perform some time-consuming tasks, such as data calculations, network requests, etc. without blocking the main thread. In this way, the page will not be "stuck" because the script is executed for too long, and the user experience will naturally be better.

What is a Web Worker?

Simply put, Web Worker is a JavaScript file that runs independently in the browser background. It runs on different threads from the main page, so it will not affect the page's response speed.

You may encounter a situation where a complex computing task makes the entire page stutter, the buttons are not clicked, and the animation is stopped, because JS is executed by a single thread. Web Worker is here to solve this problem.

It should be noted that Worker cannot operate the DOM directly, nor can it use window or document objects. Its operating environment is relatively independent and can only communicate with the main thread through the message mechanism.

How to create and use Web Worker?

To use Web Worker, you first need to create a separate JS file that writes the code you want to run in the background. Then instantiate a Worker object in the main page and pass the data through postMessage and onmessage .

For example:

 // main.js
const worker = new Worker('worker.js');

worker.onmessage = function(event) {
  console.log('Received message:', event.data);
};

worker.postMessage('Start Work');

 // worker.js
onmessage = function(event) {
  console.log('Worker received:', event.data);
  postMessage('Task Complete');
}

This completes the most basic Worker message interaction. In practical applications, you can place complex calculations, polling, timing tasks, etc. here to execute.

What common problems can Web Worker solve?

• Long-term tasks cause page stuttering
  For example, encryption and decryption, image processing, large-scale data sorting, etc., these can be put into the Worker to perform.

• Avoid blocking user interaction
  If your page has timers or long loop tasks, putting it in the main thread will seriously affect the UI response, and Worker is very suitable at this time.

• Handle multiple tasks in parallel
  Although JavaScript itself is single-threaded, Web Worker allows you to achieve "pseudo-multi-threaded" effects and improve overall performance.

Of course, not all tasks are suitable for worker. For example, tasks involving frequent DOM updates are not suitable because Worker cannot operate the DOM directly.

Notes on using Web Worker

• Worker cannot load scripts across domains and must come from the same source.
• Synchronous blocking methods such as alert() or confirm() cannot be used in Worker.
• Message delivery is asynchronous, so pay attention to structured cloning restrictions (such as not being able to pass functions).
• Don't abuse Workers, each Workers will take up extra memory and resources.

If you are just doing some simple delay or timing tasks, you don't need to use Worker. But if it involves a lot of computing or long-running logic, it is worth considering moving it to the backend to do it.

Basically that's it. Web Worker is not complicated, but can easily be overlooked, especially in the early stages of development. When you find that the page is slowing down but cannot find obvious bottlenecks, it may be time to consider using Worker to move some tasks out.

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