Exception when run in a WebWorker

[ligaz]

Trying to execute Prism.highlight(...) in a WebWorker results in an error being throw from Prism.

It looks like the following code is the culprit. It assumes that if Prism is run in a Worker it will a be Worker created by itself using the async option and the message will have the Prism contract being a JSON with language, code and immediateClose fields.

[Golmote]

Can you provide some example code to reproduce the issue? Prism should be able to be used in a Worker. I just tested the following code, that works:

    var worker = new Worker('prism.js');
    worker.onmessage = function(evt) {
        console.log(evt.data);
        // Displays <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>span</span><span class="token punctuation">></span></span>
    };
    worker.postMessage(JSON.stringify({
        language: 'markup',
        code: '<span>'
    }));

[Rob--W]

@Golmote Look at the code linked from the report. It is quite obvious that it unconditionally handles any messages. That makes Prism.js in its current form unsuitable as a library in a Web worker (opposed to being the sole and only script running in the worker, as the code currently assumes).

I worked around the issue in my own project by temporarily clearing the addEventListener method because then prism.js will not attach a global message listener (ref in prism source): https://github.com/Rob--W/crxviewer/blob/ce1c9ec1bd5dc61f6d302ba835b76c16418d9ac0/src/lib/prettify/prism-source-extensions.js#L8-L14

Ideally there would be a global flag to disable this, e.g. _self.prismAsWorkerLib (if this is set, then Prism.js will not attach a message handler).

[Golmote]

Could we add a public method to detach the message listener? Would this help?

[ligaz]

Ideally the onmessage handler should be installed in case Prism.highlightElement is run with async option: https://github.com/PrismJS/prism/blob/gh-pages/components/prism-core.js#L212

[ligaz]

You can also check the format of the incoming message and do nothing if it cannot be processed.

[Rob--W]

Ideally the onmessage handler should be installed in case Prism.highlightElement is run with async option: https://github.com/PrismJS/prism/blob/gh-pages/components/prism-core.js#L212

The onmessage handler must be registered in the worker, not in the main thread, so this does not work unless you plan on creating a dynamic worker script.

[ligaz]

@Rob--W True that. There are ways to hack this around (like passing arguments via location) but they are not stable.