What is this?

Experimental ClojureScript's compiler extension that enables JavaScript's async/await through async blocks and await, await-all & await-first operators.

Requires :language-in compiler option set to :ecmascript-2017 or newer ECMAScript versions, this will set :language-out to the same version. When targeting JavaScript runtimes where async/await is not supported, set :language-out to appropriate version and Google Closure Compiler will compile it down into supported implementation.

Usage

(require '[async-await.core :refer [async await]])

(defn http-get [url]
  (async
    (let [response (await (js/fetch url))
          json (await (.json response))]
      (.log js/console json))))

Limitations

JavaScript's await statement is not allowed in non-async functions, this causes a problem because of ClojureScript's codegen. When translated into JavaScript, constructs like the one below emit self-invoking function in place of do.

(async
  (let [x (do (inc 1) (await 2))]
    x))

Output:

(async function() {
  var x = (function() {
    1 + 1;
    return await 2;
  })();
  return x;
})()

API

• async wraps body into self-invoking JavaScript's async function, returns promise
• await suspends execution of current async block and returns asynchronously resolved value
• await-all same as (seq (.all js/Promise coll)), but for easier usage within async blocks
• await-first same as (.race js/Promise coll), but for easier usage within async blocks

Tests

clojure -A:test -m cljs.main -m async-await.core-test -re node