As someone that worked at the company that taught Pete Hunt, and other early contributors to react this trick, I wouldn't call it a benefit, but the only workable solution to acceptable single page web application performance in an otherwise terrible development environment (browser javascript).

Proper concurrency support and real mutexes would be way better than having a single execution thread for all your computations that is shared with all the visual and human interaction computations. Plus, the data sharing models between the main thread and web workers is pretty crap for anything serious, so it's not even easy to get computations out of the main thread that don't need to be there.

I don’t think I agree. I can’t think of many tasks I’ve ever tried to solve in programming where moving the work to another thread was the right answer. Usually things are too entangled, or too fast to bother. And there’s so much overhead in threading - from thread creation and destruction, message passing with mutexes or whatever and you need to figure out how to share data in a way that doesn’t accidentally give you lower overall performance for your trouble. I’d rather spend the same time just optimising the system so it doesn’t need it’s own thread in the first place.

The mostly single threaded / async model is a hassle sometimes. But I find it much easier to reason about because I know the rest of my program has essentially paused during the current callback’s execution.

I've also found few use cases for workers in the browser, but as the parent pointed out that's partly because of the limited and sluggish communication between threads in javascript. Just to offer an opposite perspective, serverside, almost any modestly heavy processing I do with nodejs happens in worker threads. These are pooled so they don't need to spin up. Blocking node's event loop is never an option. Fine to access a big dataset with an async call, but if you need to crunch that data before passing it to the client you pretty much have to use workers. [edit] obviously assuming you're not calling some command line process, and you're trying to chew though some large rendering of data using JS.

I find Clojurescript to have a superb async support and ecosystem.

Like everyone getting frustrated with the buggy core.async and just using JS promises directly?

In Clojure/JVM core.async has less problems though.

Never ran into problems when I was using it ~5 years ago.

I'm not very familiar with concurrency at a lower level, so I can't comment on your complaints. What Clojurescript provides is considerably better abstractions that in turn get you correct implementations with much less incidental complexity or hassle.

Not sure why my sincere question about the state of browser execution environment got downvoted, but the general concerns I raised in my first comment weren't about incidental complexity or hassle. They matter and it's great that clojurescript helps with those two. The concern I voiced was about maintaining realtime performance of a responsive user interface. The key issue is that you have a single event loop that all visual and human interactions need to be handled by because that's the only thread that can interact with the DOM. It's just way too easy to block that thread and cause the app to become unresponsive.

> The key issue is that you have a single event loop that all visual and human interactions need to be handled by because that's the only thread that can interact with the DOM.

Isn't that normal? A single event/drawing loop. Would there be an advantage to two threads drawing? Sounds pretty novel.