clojurescript中core.async的优点是什么？

Question

每个人都在谈论core.async有多棒,以及如何改进clojurescript中的事件处理.我一直在关注ClojureScript 101教程,我没有从这些代码示例中看到任何明显的优势.我错过了什么？

为什么在这里使用core.async更好？

(defn listen [el type]
  (let [out (chan)]
    (events/listen el type
      (fn [e] (put! out e)))
    out))

(defn dosomethingasync
  [e]
  (js/console.log "async: " e))

(let [clicks (listen (dom/getElement "search1") "click")]
  (go (while true (dosomethingasync (<! clicks)))))

与

(defn dosomethingcallback
   [e]
   (js/console.log "callback: " e))

(events/listen (dom/getElement "search2") "click" dosomethingcallback)

Answer 1

好问题!

我认为你了解其优势的第一步将是Timothy Baldridge Video

在我的尝试之下:

我认为如果我们改变你的代码,差异就会消失.

首先,尝试突出显示句子"在组件或子系统必须停止直接相互通信的所有优秀程序中的时间"从clojure博客上发布的core.async的表示中提取.我认为我们可以将输入事件通道与let fn分开:

(def clicks (listen (dom/getElement "search1") "click"))

(go
  (while true
    (dosomethingasync (<! clicks))))

(put! clicks "this channel can be written from differents parts of your code")

其次,使用core.async,我们可以编写异步调用,因为我们将编写同步调用(顺序代码).这种情况的一个示例需要多个通道:

(def clicks (listen (dom/getElement "search1") "click"))

(def keys-pressed (listen (dom/getElement "search1") "keypress"))

(def to-out (chan))

(go
  (while true
    (let [click-recieved (<! clicks)]
      (dosomethingasync click-recieved)
      (>! to-out "click recieved!")
      (let [other-input-waited (<! keys-pressed)]
        (dosomethingwithkey other-input-waited)
        (>! to-out "keypressed recieved!")
        )
      )
    ))

最后,我认为你没有正确使用回调函数的含义.当我们谈论回调函数时,我认为我们指的是一个函数,除了它自己的参数外,它还接收一个函数"callback".在函数执行结束时,我们调用回调函数将执行流程返回到原始点.更改"回调"功能如下:

(defn dosomethingcallback
   [e call-back-fn]
   (js/console.log "callback: " e)
   (call-back-fn))

如果我们尝试发布类似于以前的代码core.async示例所实现的相同行为:

(defn do-key
   [call-back-fn e]
   (.log js/console "before  callback key" )
   (call-back-fn e))

(defn do-click
   [call-back-fn e]
   (.log js/console "before callback click")
   (call-back-fn e))

(defn key-callback-fn [e]
  (.log js/console (str "doing some work with this key: " e))
  )

(defn click-callback-fn [e]
  (.log js/console (str "doing some work with this click" e))
  (events/listen (dom/getElement "search2") "keypress" (partial do-key key-callback-fn)))


  (events/listen (dom/getElement "search2") "click" (partial do-click click-callback-fn))