Introduction to Web Workers for background tasks
Webworkers in JavaScript programming allow programmers to run JavaScript program source code externally in the background from the main thread, which helps the programmer to complete resource-intensive tasks without stopping the user interface UI in programming. Webworkers in JavaScript are very helpful for programming tasks such as managing and controlling system data processing, network requests, or any large numeric data calculation processing.
Sometimes, running heavy system operations on the main thread in a network system task can cause system performance related issues. Such as, the system becoming unresponsive in the network, especially in web application tasks with rich interaction. Here Web Worker enables Internet users to offload or run such tasks on a separate thread, which ensures that the UI is more responsive while the background task is running.
What is Web Worker in JavaScript?
In JavaScript programming, a web worker is a JavaScript source based created script, which runs in the background on a thread separate from the main UI thread in the current program. Web workers in JavaScript can be used to perform system calculations or tasks or to manage complex tasks without affecting the existing system user interface. While the web worker cannot access the DOM (Document Object Model) in the thread, it can communicate and control with the main thread through messages.
Why use web workers in JavaScript?
- In JavaScript, CPU-intensive calculations have to be done in heavy system tasks separate from the main thread. Such as, mathematical numeric calculations, image editing manipulation, etc.
- Data processing has to be done for large datasets in JavaScript webpages. Such as, parsing large JSON files in a webpage or program or controlling array databases in large volumes.
- Sometimes JavaScript webpages may have asynchronous network requests that take a long time, ensuring that the complete UI remains responsive in the system.
- Web worker is an important feature in JavaScript for real-time data streaming processing. Such as, WebSocket, displaying real-time updates, etc.
- The important role of web worker in JavaScript programming is that it provides a multitasking system environment without blocking a separate UI thread without disturbing the main system processing.
Creating Basic Web Worker in JavaScript Programming.
To create a basic web worker in JavaScript programming, the programmer has to create and write a separate JavaScript file for the web worker. Where there is a program source code to be executed in the background separately from the main system. This main thread communicates with the web worker through the postMessage() function method.
Step-by-step to create a web worker in JavaScript.
Create web worker (worker.js) – First of all create worker.js file. This file contains the program source code, which is executed in a separate worker thread.
// let we create worker.js file for sepret thread as backgrund task
self.onmessage = function (systemevent) {
const output = systemevent.data * 2; // here it example, that doubling the received number
self.postMessage(output); // here it Send the result back to the main thread with background task
};
Here self object indicates the web worker task itself.
Here onmessage reads the message sent from the systemevent main thread.
While postMessage() method is used to send system data back to the main thread.
Here main thread (index.html or main.js) – In this file web worker task is created and used.
<!– index.html –>
<script>
// let here we Create a sample web worker from the worker.js file
const worker = sample Worker(‘worker.js’);
// let here we Send data to the worker js file (as a number to be doubled)
worker.postMessage(4);
// here it use to Listen for a web worker response from the web worker
worker.onmessage = function (event) {
const output = event.data; // here it used to Received doubled value from postmessage
console.log(‘output from the web worker’, output); // Result – output from the web worker 8
};
// here it used to Error handling in case of web worker task failure
worker.onerror = function (error) {
console.error(‘display Error in web worker’, error.message);
};
</script>
Here sample Worker(‘worker.js’) creates a new instance of the web worker.
Here postMessage() method sends a message to the web worker.
Here onmessage event is executed when the web worker sends a return message to the main thread.
Passing messages between main thread and worker in JavaScript file.
In any JavaScript web worker file, main thread and web worker can communicate by applying postMessage() and onmessage method. Where data is sent by sending messages, and here both these processes can run in synchronous or asynchronous task order, it depends on the condition how user sets the message listener.
we use Main Thread to Sends Data to web Worker
// let create a Main thread
worker.postMessage({ action: “handleData”, data: [19, 28, 73, 10] });
here Worker used to Sends Data Back to Main Thread side
// here Worker thread created
self.postMessage({ output: processedData });
Handling Responses in Main Thread
// here we create a Main thread listens for the message to listen
worker.onmessage = function (event) {
const output = event.data.output;
console.log(“Data handle”, output);
};
Terminating and Managing Web Workers in JavaScript.
After a created web worker is used in a JavaScript program, the user should terminate it to empty the system resources. For this, programmers can apply the terminate() function method from the main thread.
/ Web Worker Main Thread
worker.terminate();
Important – Here, after the web worker is terminated, the worker cannot communicate with the main thread in any way.
Proper web worker termination.
It can also terminate itself by calling the close() function in the web worker script.
/ worker.js
self.close(); // It can also terminate the worker from within itself
Error management with JavaScript web workers.
Errors in a JavaScript web worker file can be caught by the onerror event handler.
/ Web Worker Main Thread: Error Management
worker.onerror = function (error) {
console.error(“display error in web worker”, error.message);
};
Errors in the thread generated in the web worker file can be caught, and returned and reported to the main thread, allowing programmers to manage them in the proper order.
Limitations of web workers created in JavaScript.
- No DOM access – Web workers in JavaScript programs do not have direct access to the DOM or window object. Here web workers can only interact or communicate with the main thread through message passing.
- No synchronous API – Here web workers cannot access synchronous APIs like alert() or prompt() method, as these are run in a separate thread in the background.
- Same-origin policy – Here web worker scripts should be served from the same origin as the main webpage. Due to security reasons, users cannot load web workers from a different domain unless CORS headers are configured in the proper order.
- Performance overhead – Web workers in JavaScript programming help in multitasking programming concept, but sometimes creating too many web workers or excessive communication between web workers and main thread causes system overhead or delay.
Conclusion of Webworker in JavaScript.
By creating web workers in JavaScript programming, one can perform deep system tasks in multitasking computational order without blocking the main UI thread, resulting in web applications being created in a proper or smoother and more responsive order. Web workers in JavaScript programming are a powerful tool or feature for multiple tasks, such as parallel processing of large volume data sets at the same time, offloading large volume or heavy-duty calculations or background tasks, or managing and controlling real-time data processing updates in the system network.
