* add js-global? helper to analyzer

* in host call check for this case
  - if js global change the type resolution via externs
* add some comment eval exprs for context

Author: swannodette

src/main/clojure/cljs/analyzer.cljc

@@ -3542,6 +3542,12 @@
                  (list* '. dot-form) " with classification "
                  (classify-dot-form dot-form))))))
 
+(defn js-global?
+  "Return true if the expr is a JS global"
+  [expr]
+  (and (= 'js (:ns expr))
+       (some? (get-in (get-externs) [(-> (:name expr) name symbol)]))))
+
 (defn analyze-dot [env target field member+ form]
   (let [v [target field member+]
         {:keys [dot-action target method field args]} (build-dot-form v)
@@ -3550,11 +3556,14 @@
         form-meta  (meta form)
         target-tag (:tag targetexpr)
         prop       (or field method)
-        tag        (or (:tag form-meta)
-                       (and (js-tag? target-tag)
-                            (vary-meta (normalize-js-tag target-tag)
-                              update-in [:prefix] (fnil conj '[Object]) prop))
-                       nil)]
+        tag        (if (js-global? targetexpr)
+                     ;; we have a known global, don't treat as instance of some type
+                     (with-meta 'js {:prefix [(-> targetexpr :name name symbol) prop]})
+                     (or (:tag form-meta)
+                         (and (js-tag? target-tag)
+                              (vary-meta (normalize-js-tag target-tag)
+                                update-in [:prefix] (fnil conj '[Object]) prop))
+                         nil))]
     (when (and (not= 'constructor prop)
                (not (string/starts-with? (str prop) "cljs$"))
                (not (-> prop meta :protocol-prop)))

src/main/clojure/cljs/compiler.cljc

@@ -641,7 +641,7 @@
 
 (defn safe-test? [env e]
   (let [tag (ana/infer-tag env e)]
-    (or (#{'boolean 'seq} tag) (truthy-constant? e))))
+    (or ('#{boolean seq js/Boolean} tag) (truthy-constant? e))))
 
 (defmethod emit* :if
   [{:keys [test then else env unchecked]}]

src/main/clojure/cljs/externs.clj

@@ -432,5 +432,6 @@
     (get 'React)
     (find 'Component) first meta)
 
+  (info (externs-map) '[Number])
   (-> (info (externs-map) '[Number isNaN]) :ret-tag) ;; => boolean
   )

src/test/clojure/cljs/externs_parsing_tests.clj

@@ -48,16 +48,35 @@
                (find 'HTMLDocument) first meta)]
     (is (= 'Document (:super info)))))
 
-;; TODO:
-;; analyze (.isNaN js/NaN 1)
-;; node :tag should be js/Boolean
+(deftest test-number-infer-test
+  (let [cenv (env/default-compiler-env)
+        aenv (ana/empty-env)]
+    (is (= (env/with-compiler-env cenv
+             (:tag (ana/analyze aenv '(.isNaN js/Number 1))))
+           'js/Boolean))))
+
+;; TODO: js/subtle.crypto
 
 (comment
 
+  (externs/info
+    (::ana/externs @(env/default-compiler-env))
+    '[Number])
+
+  (externs/info
+    (::ana/externs @(env/default-compiler-env))
+    '[Number isNaN])
+
   ;; js/Boolean
   (env/with-compiler-env (env/default-compiler-env)
     (ana/js-tag '[Number isNaN] :ret-tag))
 
+  ;; js
+  (let [cenv (env/default-compiler-env)
+        aenv (ana/empty-env)]
+    (->> (env/with-compiler-env cenv
+           (:tag (ana/analyze aenv '(.isNaN js/Number 1))))))
+
   (externs/parse-externs
     (externs/resource->source-file (io/resource "goog/object/object.js")))