How can one determine if script has been included in a Web Worker?

Question

I'd like to set up my library to "just work" as a Web Worker if spun up in a new Worker() . To do so I need to attach an event listener on self to receive messages.

If my script has been included inside another developer's Web Worker using an importScripts() , how do I know when I'm a third party and should not attach an event listener on self to receive messages?

Answer 1

You may try like this using WorkerGlobalScope :

if (typeof WorkerGlobalScope !== 'undefined' && self instanceof WorkerGlobalScope) {
    // code
} else {
    // code
}

ie, you may check for the absence of document to check you're in a worker.

Also the specs says that:

The DOM APIs (Node objects, Document objects, etc) are not available to workers in this version of this specification.