Peter Lubbers - Pro HTML 5 Programming

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CHAPTER 8 ■ USING THE HTML5 WEB WORKERS API
Browser Support for HTML5 Web Workers
Browser support for Web Workers is at varying stages and will continue to evolve. As shown in Table 8-1,
Web Workers is already supported in many browsers at the time of this writing.
Table 8-1. Opera Supported in version 10.6 and greater
Browser Details
Chrome Supported in version 3 and greater
Firefox Supported in version 3.5 and greater
Internet Explorer Not supported (yet)
Opera Supported in version 10.6 and greater
Safari Supported in version 4 and greater
Using the HTML5 Web Workers API
In this section, we’ll explore the use of the Web Workers API in more detail. For the sake of illustration,
we’ve created a simple browser page: echo.html. Using Web Workers is fairly straightforward—you
create a Web Worker object and pass in a JavaScript file to be executed. Inside the page you set up an
event listener to listen to incoming messages and errors that are posted by the Web Worker and if you
want to communicate from the page to the Web Worker, you call postMessage to pass in the required
data. The same is true for the code in the Web Worker JavaScript file—event handlers must be set up to
process incoming messages and errors, and communication with the page is handled with a call to
postMessage.
Checking for Browser Support
Before you call the Web Workers API functions, you will want to make sure there is support in the
browser for what you’re about to do. This way, you can provide some alternate text, prompting the users
of your application to use a more up-to-date browser. Listing 8-1 shows the code you can use to test for
browser support.
Listing 8-1. Checking for browser support
function loadDemo() {
if (typeof(Worker) !== "undefined") {
document.getElementById("support").innerHTML =
"Excellent! Your browser supports HTML5 Web Workers";
}
}