diff --git a/src/reagent/core.cljs b/src/reagent/core.cljs
index 396a42d..a9d6e8e 100644
--- a/src/reagent/core.cljs
+++ b/src/reagent/core.cljs
@@ -64,33 +64,39 @@ Everything is optional, except :render.
 (defn state
   "Returns the state of a component, as set with replace-state or set-state."
   [this]
+  (assert (util/reagent-component? this))
   (comp/state this))
 
 (defn replace-state
   "Set state of a component."
   [this new-state]
+  (assert (util/reagent-component? this))
   (comp/replace-state this new-state))
 
 (defn set-state
   "Merge component state with new-state."
   [this new-state]
+  (assert (util/reagent-component? this))
   (comp/set-state this new-state))
 
 
 (defn props
   "Returns the props passed to a component."
   [this]
-  (comp/get-props this))
+  (assert (util/reagent-component? this))
+  (util/get-props this))
 
 (defn children
   "Returns the children passed to a component."
   [this]
-  (comp/get-children this))
+  (assert (util/reagent-component? this))
+  (util/get-children this))
 
 (defn argv
   "Returns the entire Hiccup form passed to the component."
   [this]
-  (comp/get-argv this))
+  (assert (util/reagent-component? this))
+  (util/get-argv this))
 
 (defn dom-node
   "Returns the root DOM node of a mounted component."
diff --git a/src/reagent/impl/component.cljs b/src/reagent/impl/component.cljs
index 457750d..4dae8d2 100644
--- a/src/reagent/impl/component.cljs
+++ b/src/reagent/impl/component.cljs
@@ -10,7 +10,7 @@
 (def cljs-state "cljsState")
 (def cljs-render "cljsRender")
 
-;;; Accessors
+;;; State
 
 (defn state [this]
   (aget this cljs-state))
@@ -26,37 +26,14 @@
 (defn set-state [this new-state]
   (replace-state this (merge (state this) new-state)))
 
-(defn js-props [C]
-  (aget C "props"))
-
-(defn extract-props [v]
-  (let [p (get v 1)]
-    (if (map? p) p)))
-
-(defn extract-children [v]
-  (let [p (get v 1)
-        first-child (if (or (nil? p) (map? p)) 2 1)]
-    (if (> (count v) first-child)
-      (subvec v first-child))))
-
-(defn get-argv [C]
-  (-> C js-props (aget cljs-argv)))
-
-(defn get-props [C]
-  (-> C get-argv extract-props))
-
-(defn get-children [C]
-  (-> C get-argv extract-children))
-
 
 ;;; Rendering
 
-
 (defn do-render [C]
   (binding [*current-component* C]
     (let [f (aget C cljs-render)
           _ (assert (ifn? f))
-          p (js-props C)
+          p (util/js-props C)
           res (if (nil? (aget C "componentFunction"))
                 (f C)
                 (let [argv (aget p cljs-argv)
@@ -77,7 +54,7 @@
           res)))))
 
 
-;;; Function wrapping
+;;; Method wrapping
 
 (defn custom-wrapper [key f]
   (case key
@@ -100,7 +77,7 @@
       (this-as C
                ;; Don't care about nextstate here, we use forceUpdate
                ;; when only when state has changed anyway.
-               (let [inprops (js-props C)
+               (let [inprops (util/js-props C)
                      old-argv (aget inprops cljs-argv)
                      new-argv (aget nextprops cljs-argv)]
                  (if (nil? f)
diff --git a/src/reagent/impl/template.cljs b/src/reagent/impl/template.cljs
index 9be0f30..26804e4 100644
--- a/src/reagent/impl/template.cljs
+++ b/src/reagent/impl/template.cljs
@@ -43,13 +43,6 @@
           (coll? v) (clj->js v)
           :else (fn [& args] (apply v args)))))
 
-(defn extract-props [v]
-  (let [p (get v 1)]
-    (if (map? p) p)))
-
-(defn get-props [this]
-  (-> this (aget "props") (aget cljs-argv) extract-props))
-
 (defn undash-prop-name [n]
   (or (attr-aliases n)
       (util/dash-to-camel n)))
@@ -94,12 +87,12 @@
 ;;; Specialization for input components
 
 (defn input-initial-state [this]
-  (let [props (get-props this)]
+  (let [props (util/get-props this)]
     #js {:value (:value props)
          :checked (:checked props)}))
 
 (defn input-handle-change [this e]
-  (let [props (get-props this)
+  (let [props (util/get-props this)
         on-change (or (props :on-change) (props "onChange"))]
     (when-not (nil? on-change)
       (let [target (.-target e)]
@@ -108,7 +101,7 @@
       (on-change e))))
 
 (defn input-will-receive-props [this new-props]
-  (let [props (-> new-props (aget cljs-argv) extract-props)]
+  (let [props (-> new-props (aget cljs-argv) util/extract-props)]
     (.setState this #js {:value (:value props)
                          :checked (:checked props)})))
 
@@ -127,7 +120,7 @@
 (declare as-component)
 
 (defn wrapped-render [this comp id-class input-setup]
-  (let [inprops (aget this "props")
+  (let [inprops (util/js-props this)
         argv (aget inprops cljs-argv)
         props (get argv 1)
         hasprops (or (nil? props) (map? props))
@@ -144,7 +137,7 @@
     (.apply comp nil jsargs)))
 
 (defn wrapped-should-update [C nextprops nextstate]
-  (let [inprops (aget C "props")
+  (let [inprops (util/js-props C)
         a1 (aget inprops cljs-argv)
         a2 (aget nextprops cljs-argv)]
     (not (util/equal-args a1 a2))))
diff --git a/src/reagent/impl/util.cljs b/src/reagent/impl/util.cljs
index b7b4424..91bc2ae 100644
--- a/src/reagent/impl/util.cljs
+++ b/src/reagent/impl/util.cljs
@@ -6,9 +6,38 @@
 (def is-client (not (nil? (try (.-document js/window)
                                (catch js/Object e nil)))))
 
+(def React reactimport/React)
+
+;;; Props accessors
+
+(def props "props")
 (def cljs-level "cljsLevel")
 (def cljs-argv "cljsArgv")
-(def React reactimport/React)
+
+(defn js-props [C]
+  (aget C props))
+
+(defn extract-props [v]
+  (let [p (get v 1)]
+    (if (map? p) p)))
+
+(defn extract-children [v]
+  (let [p (get v 1)
+        first-child (if (or (nil? p) (map? p)) 2 1)]
+    (if (> (count v) first-child)
+      (subvec v first-child))))
+
+(defn get-argv [C]
+  (-> C (aget props) (aget cljs-argv)))
+
+(defn get-props [C]
+  (-> C (aget props) (aget cljs-argv) extract-props))
+
+(defn get-children [C]
+  (-> C (aget props) (aget cljs-argv) extract-children))
+
+(defn reagent-component? [C]
+  (-> C get-argv nil? not))
 
 
 ;; Misc utilities