core.cljs

(ns foo.core
  (:require-macros [foo.macros :refer [with-open]])
  (:require [cljs.nodejs :as nodejs]))

(nodejs/enable-util-print!)

(def foo
  (reify
    Object
    (close [_] (println "closing!"))))

; (with-open [f foo] (+ 1 1)) ;=> #object[TypeError TypeError: Cannot read property 'macros' of undefined]



(defn -main [& args] nil)
(set! *main-cli-fn* -main)

macros.cljc

(ns foo.macros
   (:refer-clojure :exclude [with-open]))

(defmacro with-open
  "bindings => [name init ...]
  Evaluates body in a try expression with names bound to the values
  of the inits, and a finally clause that calls (.close name) on each
  name in reverse order."
  [bindings & body]
  (assert (vector? bindings) "a vector for its binding")
  (assert (even? (count bindings)) "an even number of forms in binding vector")
  (cond
    (= (count bindings) 0) `(do ~@body)
    (symbol? (bindings 0)) `(let ~(subvec bindings 0 2)
                              (try
                                (with-open ~(subvec bindings 2) ~@body)
                                (finally
                                  (. ~(bindings 0) close))))
    :else  (throw #?(:cljs (js/Error. "with-open only allows Symbols in bindings")
                     :clj  (IllegalArgumentException.
                                      "with-open only allows Symbols in bindings")))))