To follow up on my prior request, I think soon I'll be exploring implementing a new PR to CLJS for a new target, :with-webworker which will spit out both a main.js and a main-worker.js, so that an in core spawn fn (or one provided in a lib) can depend on there being a shim available. Or maybe just always produce the shim for every build if it's really cheap. Reason being, in-mesh is shaping up to be pretty powerful:

(let [a @(future 1)
      b @(future 2)
      c @(future 3)]
  (println :values [a b c])
  [a b c])
;:values [1 2 3]
;=> [1 2 3]

(defn flip [n]
  (apply comp (take n (cycle [inc dec]))))

(->> (range 1000000)
     (map (flip 100))
     (filter odd?)
     (map (flip 100))
     (map inc)
     (map (flip 100))
     (apply +)
     (println)
     time)
;"Elapsed time: 11452.300000 msecs"
;=> 250000500000

(=>> (range 1000000)
     (map (flip 100))
     (filter odd?)
     (map (flip 100))
     (map inc)
     (map (flip 100))
     (apply +)
     (println)
     time)
;"Elapsed time: 5615.500000 msecs"
;=> 250000500000