When executing scripts in an HTML page, the page becomes unresponsive until the script is finished.
The numbers in the table specify the first browser version that fully support Web Workers.
The example below creates a simple web worker that count numbers in the background:
Before creating a web worker, check whether the user's browser supports it:
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.
Note: Normally web workers are not used for such simple scripts, but for more CPU intensive tasks.
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":
Then we can send and receive messages from the web worker.
Add an "onmessage" event listener to the web worker.
When the web worker posts a message, the code within the event listener is executed. The data from the web worker is stored in event.data.
When a web worker object is created, it will continue to listen for messages (even after the external script is finished) until it is terminated.
To terminate a web worker, and free browser/computer resources, use the
If you set the worker variable to undefined, after it has been terminated, you can reuse the code:
We have already seen the Worker code in the .js file. Below is the code for the HTML page: