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Oct 21, 2013 · 1. Yes you can definitely use ajax in web worker by simply using XML Http Request or fetch API and can post the message using postmessage by using my code hope it helps:->. #Declaring Worker. document.body.innerHTML=data.data; #Web Worker Code. .then(response => { return response.text(); })
- Overview
- Web Workers API
- Dedicated workers
- Shared workers
- About thread safety
- Content security policy
- Transferring data to and from workers: further details
- Embedded workers
- Further examples
Web Workers are a simple means for web content to run scripts in background threads. The worker thread can perform tasks without interfering with the user interface. In addition, they can make network requests using the fetch() or XMLHttpRequest APIs. Once created, a worker can send messages to the JavaScript code that created it by posting messages to an event handler specified by that code (and vice versa).
This article provides a detailed introduction to using web workers.
A worker is an object created using a constructor (e.g. Worker()) that runs a named JavaScript file — this file contains the code that will run in the worker thread; workers run in another global context that is different from the current window. Thus, using the window shortcut to get the current global scope (instead of self) within a Worker will return an error.
The worker context is represented by a DedicatedWorkerGlobalScope object in the case of dedicated workers (standard workers that are utilized by a single script; shared workers use SharedWorkerGlobalScope). A dedicated worker is only accessible from the script that first spawned it, whereas shared workers can be accessed from multiple scripts.
You can run whatever code you like inside the worker thread, with some exceptions. For example, you can't directly manipulate the DOM from inside a worker, or use some default methods and properties of the window object. But you can use a large number of items available under window, including WebSockets, and data storage mechanisms like IndexedDB. See Functions and classes available to workers for more details.
Data is sent between workers and the main thread via a system of messages — both sides send their messages using the postMessage() method, and respond to messages via the onmessage event handler (the message is contained within the message event's data attribute). The data is copied rather than shared.
Workers may in turn spawn new workers, as long as those workers are hosted within the same origin as the parent page.
In addition, workers can make network requests using the fetch() or XMLHttpRequest APIs (although note that the responseXML attribute of XMLHttpRequest will always be null).
As mentioned above, a dedicated worker is only accessible by the script that called it. In this section we'll discuss the JavaScript found in our Basic dedicated worker example (run dedicated worker): This allows you to enter two numbers to be multiplied together. The numbers are sent to a dedicated worker, multiplied together, and the result is returned to the page and displayed.
This example is rather trivial, but we decided to keep it simple while introducing you to basic worker concepts. More advanced details are covered later on in the article.
A shared worker is accessible by multiple scripts — even if they are being accessed by different windows, iframes or even workers. In this section we'll discuss the JavaScript found in our Basic shared worker example (run shared worker): This is very similar to the basic dedicated worker example, except that it has two functions available handled by different script files: multiplying two numbers, or squaring a number. Both scripts use the same worker to do the actual calculation required.
Here we'll concentrate on the differences between dedicated and shared workers. Note that in this example we have two HTML pages, each with JavaScript applied that uses the same single worker file.
The Worker interface spawns real OS-level threads, and mindful programmers may be concerned that concurrency can cause "interesting" effects in your code if you aren't careful.
However, since web workers have carefully controlled communication points with other threads, it's actually very hard to cause concurrency problems. There's no access to non-threadsafe components or the DOM. And you have to pass specific data in and out of a thread through serialized objects. So you have to work really hard to cause problems in your code.
Workers are considered to have their own execution context, distinct from the document that created them. For this reason they are, in general, not governed by the content security policy of the document (or parent worker) that created them. So for example, suppose a document is served with the following header:
Among other things, this will prevent any scripts it includes from using eval(). However, if the script constructs a worker, code running in the worker's context will be allowed to use eval().
To specify a content security policy for the worker, set a Content-Security-Policy response header for the request which delivered the worker script itself.
The exception to this is if the worker script's origin is a globally unique identifier (for example, if its URL has a scheme of data or blob). In this case, the worker does inherit the CSP of the document or worker that created it.
Data passed between the main page and workers is copied, not shared. Objects are serialized as they're handed to the worker, and subsequently, de-serialized on the other end. The page and worker do not share the same instance, so the end result is that a duplicate is created on each end. Most browsers implement this feature as structured cloning.
To illustrate this, let's create a function named emulateMessage(), which will simulate the behavior of a value that is cloned and not shared during the passage from a worker to the main page or vice versa:
A value that is cloned and not shared is called message. As you will probably know by now, messages can be sent to and from the main thread by using postMessage(), and the message event's data attribute contains data passed back from the worker.
example.html: (the main page):
my_task.js (the worker):
The structured cloning algorithm can accept JSON and a few things that JSON can't — like circular references.
There is not an "official" way to embed the code of a worker within a web page, like
The embedded worker is now nested into a new custom document.worker property.
Performing computations in the background
Workers are mainly useful for allowing your code to perform processor-intensive calculations without blocking the user interface thread. In this example, a worker is used to calculate Fibonacci numbers.
Dividing tasks among multiple workers
As multicore computers become increasingly common, it's often useful to divide computationally complex tasks among multiple workers, which may then perform those tasks on multiple-processor cores.
Dec 1, 2022 · To solve this problem, we can use web workers. Web Workers. Web workers allow a script to run as a background thread. A worker runs with its own engine instance and event loop separate from the ...
Create a Web Worker File. Now, let's create our web worker in an external JavaScript. Here, we create a script that counts. The script is stored in the "demo_workers.js" file: The important part of the code above is the postMessage() method - which is used to post a message back to the HTML page.
Mar 26, 2018 · The implementation of web workers ensures safe, conflict-free execution in two ways: A distinct, isolated global environment for the worker thread, separate from the browser environment. Pass-by-copy exchange of data between main and worker threads in the postMessage () call. Each worker thread has a distinct, isolated global environment that ...
Create a Web Worker Object. Now that we have the web worker file, we need to call it from an HTML page. The following lines checks if the worker already exists, if not - it creates a new web worker object and runs the code in "demo_workers.js":
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