Guide: Web Workers JavaScript API: Quick Guide
Web workers is a JavaScript API that allows you run scripts in a separate thread from the main threadIt can come in handy if you don’t want to hinder the execution of the main scripts because of background-like scripts. The Web Workers API is supported in almost all browsers, for more detailed information, view the CanIUse documents. Before we get into the code, let’s look at some scenarios where you might want to use this API so that you can get a sense of what I meant with scripts that appear in the background.
Use cases
Let’s say there is a script for that retrieves and processes a fileIf a file is significantly large, it will take a long time to process! Which could block other scripts called later from running. If it file processing is moved to a background thread, known as the worker wire, other events are not blocked until the previous one is over. The script executed in a background worker thread is known as the worker script or just the employee For another example, imagine one large shape, arranged in tabsIt is scripted to update the controls in one tab affects some of the controls in others If the update of the other tabs takes some time, the user can cannot use the current tab continuously without putting his events on hold. This could freeze the UI, much to the user’s displeasure. Since a user cannot see the other tabs while filling out a current one, you can do this update the controls of the other tabs in a background threadThis way, the user can continue to use the current tab he is filling out, without any of the scripts being blocked by the update process of controls on other tabs. Likewise, if you find a screenplay that includes a script can block a user from using the user interface until execution is complete, consider moving it to a worker thread so that it can run in the background.
Reach and types of employees
The Web Workers API is probably one of the easiest APIs to work with. It has pretty easy methods to fix create worker threads and communicate with them from the main script The global scope of a worker thread is in a different context from the main thread. YOU cannot access the methods and properties of the view object such as alert () in a worker thread. You too cannot directly change the DOM of a working thread. But you can use many APIs covered by window, for example Promise and Fetch, in your worker thread (see full list). You can also have nested worker threads: worker threads created from a different worker thread. An employee created by another becomes one underworker There are also many types of workersThe two most important are dedicated and shared employees Dedicated employees belong to the same browsing context where their common thread belongs. However, shared workers are present in a different browser context (for example in an iframe) from the main script. In both cases the main script and the workers must be in the same domain The example herein tutorial will be about dedicated worker, which is the most common type.
API methods
See the diagram below for one quick overview of all important methods which form the Web Workers API. The Employee () constructor creates a special worker thread and returns its reference objectWe then use this object to communicate with that specific employee. The postMessage () method is used in both main and worker scripts to send data to each otherThe transmitted data is then received by the onmessage event handler. The to end() method terminates a worker thread from the main scriptThis termination is immediately: All current script execution and running scripts are canceled. The close to() method does the same thing, but it is evoked by the working thread closing itself
Sample code
Now let’s take a look at some sample code. The index.html page contains the main script in a
We start with the creating the worker thread from the main script
w = new employee (‘worker.js’);
The constructor Worker () takes the URL of the working file as an argument
Then we add an event handler for the onmessage event of the newly created worker instance to receive data from itThe data property of the e-event contains the received data.
w = new Worker (‘worker.js’); w.onmessage = (e) => {console.log (Received from employee: $ {e.data});}
Now we use postMessage () to convert send some data to the worker thread at the click of one buttonThe postMessage () method can take two arguments. The first can be of any type (string, array…). It’s the data are sent to the worker thread (or to the main script, if the method is present in the worker thread).
The second, optional parameter is a set of objects that can be used by the working threads (but not by the main script, or vice versa). These types of objects are called Transferable objects.
document.querySelector (‘button’) .onclick = () => {w.postMessage (’ john ‘);}
I just send a string value to the worker thread.
In the worker thread, we need to add an onmessage event handler that is receives the data sent by the main script at button Click. Within the handler, we merge the received string with another one and return the result to the main script.
console.info (‘worker created’); onmessage = (e) => {postMessage (Hi $ {e.data});}
Different from the main script where we had to use the w reference object refer to the specific worker thread where the script then uses the onmessage and postMessage methods is there no reference object is needed in the worker thread to point to the red thread.
The code works as follows. When the browser loads index.html, the console will display the message “employee created” as soon as the worker () constructor is executed in the main thread, creating a new employee.
When you click on the button on the page you will get the message ‘Received from employee: Hello john’ in the console, the string that was concatenated in the worker thread with the data sent to it, and then was returned to the main script
Web Workers JavaScript API: Quick Guide: benefits
Faq
Final note
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