How can I use create a Web worker from a string (which is supplied via a POST request)?
One way I can think of, but I'm not sure how to implement it, is by creating a data-URI from the server response, and passing that to the Worker constructor, but I've heard that some browsers don't allow this, because of the same origin policy.
MDN states the uncertainty about the origin policy around data URI's:
Note: The URI passed as parameter of the Worker constructor must obey the same-origin policy. There is currently disagreement among browsers vendors on whether data URIs are of the same-origin or not; Gecko 10.0 (Firefox 10.0 / Thunderbird 10.0) and later do allow data URIs as a valid script for workers. Other browsers may disagree.
Here's also a post discussing it on the whatwg.
Summary
blob:
for Chrome 8+, Firefox 6+, Safari 6.0+, Opera 15+data:application/javascript
for Opera 10.60 - 12eval
otherwise (IE 10+)
URL.createObjectURL(<Blob blob>)
can be used to create a Web worker from a string. The blob can be created using the BlobBuilder
API deprecated or the Blob
constructor.
Demo: http://jsfiddle.net/uqcFM/49/
// URL.createObjectURL
window.URL = window.URL || window.webkitURL;
// "Server response", used in all examples
var response = "self.onmessage=function(e){postMessage('Worker: '+e.data);}";
var blob;
try {
blob = new Blob([response], {type: 'application/javascript'});
} catch (e) { // Backwards-compatibility
window.BlobBuilder = window.BlobBuilder || window.WebKitBlobBuilder || window.MozBlobBuilder;
blob = new BlobBuilder();
blob.append(response);
blob = blob.getBlob();
}
var worker = new Worker(URL.createObjectURL(blob));
// Test, used in all examples:
worker.onmessage = function(e) {
alert('Response: ' + e.data);
};
worker.postMessage('Test');
Web workers are supported in the following browsers source:
This method's support is based on the support of the Blob
API and the URL.createObjectUrl
method. Blob
compatibility:
WebKitBlobBuilder
), 20+ (Blob
constructor)MozBlobBuilder
), 13+ (Blob
constructor)Blob
constructor)IE10 supports MSBlobBuilder
and URL.createObjectURL
. However, trying to create a Web Worker from a blob:
-URL throws a SecurityError.
Opera 12 does not support URL
API. Some users may have a fake version of the URL
object, thanks to this hack in browser.js
.
Opera supports data-URIs as an argument to the Worker
constructor. Note: Do not forget to escape special characters (Such as #
and %
).
// response as defined in the first example
var worker = new Worker('data:application/javascript,' +
encodeURIComponent(response) );
// ... Test as defined in the first example
Demo: http://jsfiddle.net/uqcFM/37/
eval
can be used as a fallback for Safari (<6) and IE 10.
// Worker-helper.js
self.onmessage = function(e) {
self.onmessage = null; // Clean-up
eval(e.data);
};
// Usage:
var worker = new Worker('Worker-helper.js');
// `response` as defined in the first example
worker.postMessage(response);
// .. Test as defined in the first example