check.cljs

(defn my-get
  "@param {*} m
   @param {*} k
   @return {nil|Object}"
  [m k]
  (get m k))

(defn foo
  "@param {!Object} x" ;; non-nullable
  [x] x)

(let [m {:foo 1}
      v (my-get m :foo)]
  (js/alert (foo v))) ;; type error

(defn bar
  "@param {PersistentVector} x"
  [x] x)

(bar {}) ;; type error

;; WARNING: 2 error(s), 1 warning(s), 73.5% typed
;; ERROR: JSC_TYPE_MISMATCH. actual parameter 2 of nullable.core.foo.call does not match formal parameter
;; found   : (Object|null)
;; required: Object at /Users/davidnolen/development/clojure/nullable/out/nullable/core.js line 20 : 34
;; ERROR: JSC_TYPE_MISMATCH. actual parameter 2 of nullable.core.bar.call does not match formal parameter
;; found   : cljs.core.PersistentArrayMap
;; required: (cljs.core.PersistentVector|null) at /Users/davidnolen/development/clojure/nullable/out/nullable/core.js line 27 : 28