diff --git a/ffi/shared.js b/ffi/shared.js
deleted file mode 100644
index 4734af5..0000000
--- a/ffi/shared.js
+++ /dev/null
@@ -1,4 +0,0 @@
-/** @template T */
-export class Maybe {}
-
-export class Milliseconds {}
diff --git a/spago.dhall b/spago.dhall
index 31e6b02..260fe2e 100644
--- a/spago.dhall
+++ b/spago.dhall
@@ -41,7 +41,9 @@ to generate this file without the comments in this block.
   , "prelude"
   , "simple-json"
   , "spec"
+  , "st"
   , "strings"
+  , "tailrec"
   , "transformers"
   , "tuples"
   , "unsafe-coerce"
diff --git a/src/Puppeteer.Base.purs b/src/Puppeteer.Base.purs
index 11a5949..5a4ffed 100644
--- a/src/Puppeteer.Base.purs
+++ b/src/Puppeteer.Base.purs
@@ -51,14 +51,14 @@ type Viewport =
 
 prepareViewport :: Viewport -> Foreign
 prepareViewport { deviceScaleFactor, hasTouch, height, width, isLandscape, isMobile } =
-   writeImpl
-     { deviceScaleFactor: FFI.maybeToUndefined deviceScaleFactor
-     , hasTouch: FFI.maybeToUndefined hasTouch
-     , isLandscape: FFI.maybeToUndefined isLandscape
-     , isMobile: FFI.maybeToUndefined isMobile
-     , height
-     , width
-     }
+  writeImpl
+    { deviceScaleFactor: FFI.maybeToUndefined deviceScaleFactor
+    , hasTouch: FFI.maybeToUndefined hasTouch
+    , isLandscape: FFI.maybeToUndefined isLandscape
+    , isMobile: FFI.maybeToUndefined isMobile
+    , height
+    , width
+    }
 
 --| [`PuppeteerNode`](https://pptr.dev/api/puppeteer.puppeteernode)
 foreign import data Puppeteer :: Row Type -> Type
diff --git a/src/Puppeteer.Eval.js b/src/Puppeteer.Eval.js
index 8908e34..072790f 100644
--- a/src/Puppeteer.Eval.js
+++ b/src/Puppeteer.Eval.js
@@ -1,8 +1,8 @@
-import {Page, JSHandle} from 'puppeteer'
+import { Page, JSHandle } from 'puppeteer'
 
-/** 
-* @type {(_: string) => (_: Page | JSHandle<unknown>) => (_: Array<unknown>) => Promise<unknown>}
-*/
+/**
+ * @type {(_: string) => (_: Page | JSHandle<unknown>) => (_: Array<unknown>) => Promise<unknown>}
+ */
 export const _run = s => h => a => {
   /** @type {any} */
   const f = new Function(`return (${s})(...arguments)`)
@@ -11,9 +11,9 @@ export const _run = s => h => a => {
   return ev(f, ...a)
 }
 
-/** 
-* @type {(_: string) => (_: Page | JSHandle<unknown>) => (_: Array<unknown>) => Promise<JSHandle<unknown>>}
-*/
+/**
+ * @type {(_: string) => (_: Page | JSHandle<unknown>) => (_: Array<unknown>) => Promise<JSHandle<unknown>>}
+ */
 export const _runh = s => h => a => {
   /** @type {any} */
   const f = new Function(`return (${s})(...arguments)`)
diff --git a/src/Puppeteer.Eval.purs b/src/Puppeteer.Eval.purs
index 7f4ea31..908a692 100644
--- a/src/Puppeteer.Eval.purs
+++ b/src/Puppeteer.Eval.purs
@@ -27,19 +27,19 @@ unsafeRunJsHandle0 :: forall e @r. EvalTarget e => String -> e -> Aff (Handle r)
 unsafeRunJsHandle0 js h = Promise.toAff $ _runh js (unsafeToForeign h) []
 
 unsafeRunJs1 :: forall a e @r. EvalTarget e => String -> a -> e -> Aff r
-unsafeRunJs1 js a h = Promise.toAff $ _run js (unsafeToForeign h) [unsafeToForeign a]
+unsafeRunJs1 js a h = Promise.toAff $ _run js (unsafeToForeign h) [ unsafeToForeign a ]
 
 unsafeRunJsHandle1 :: forall a e @r. EvalTarget e => String -> a -> e -> Aff (Handle r)
-unsafeRunJsHandle1 js a h = Promise.toAff $ _runh js (unsafeToForeign h) [unsafeToForeign a]
+unsafeRunJsHandle1 js a h = Promise.toAff $ _runh js (unsafeToForeign h) [ unsafeToForeign a ]
 
-unsafeRunJs2 :: forall a b e @r. EvalTarget e => String -> a -> b-> e -> Aff r
-unsafeRunJs2 js a b h = Promise.toAff $ _run js (unsafeToForeign h) [unsafeToForeign a, unsafeToForeign b]
+unsafeRunJs2 :: forall a b e @r. EvalTarget e => String -> a -> b -> e -> Aff r
+unsafeRunJs2 js a b h = Promise.toAff $ _run js (unsafeToForeign h) [ unsafeToForeign a, unsafeToForeign b ]
 
 unsafeRunJsHandle2 :: forall a b e @r. EvalTarget e => String -> a -> b -> e -> Aff (Handle r)
-unsafeRunJsHandle2 js a b h = Promise.toAff $ _runh js (unsafeToForeign h) [unsafeToForeign a, unsafeToForeign b]
+unsafeRunJsHandle2 js a b h = Promise.toAff $ _runh js (unsafeToForeign h) [ unsafeToForeign a, unsafeToForeign b ]
 
 unsafeRunJs3 :: forall a b c e @r. EvalTarget e => String -> a -> b -> c -> e -> Aff r
-unsafeRunJs3 js a b c h = Promise.toAff $ _run js (unsafeToForeign h) [unsafeToForeign a, unsafeToForeign b, unsafeToForeign c]
+unsafeRunJs3 js a b c h = Promise.toAff $ _run js (unsafeToForeign h) [ unsafeToForeign a, unsafeToForeign b, unsafeToForeign c ]
 
 unsafeRunJsHandle3 :: forall a b c e @r. EvalTarget e => String -> a -> b -> c -> e -> Aff (Handle r)
-unsafeRunJsHandle3 js a b c h = Promise.toAff $ _runh js (unsafeToForeign h) [unsafeToForeign a, unsafeToForeign b, unsafeToForeign c]
+unsafeRunJsHandle3 js a b c h = Promise.toAff $ _runh js (unsafeToForeign h) [ unsafeToForeign a, unsafeToForeign b, unsafeToForeign c ]
diff --git a/src/Puppeteer.FFI.js b/src/Puppeteer.FFI.js
index f8f389c..c3409c2 100644
--- a/src/Puppeteer.FFI.js
+++ b/src/Puppeteer.FFI.js
@@ -10,7 +10,7 @@ export const mergeRecords = rs =>
 
 /** @type {(m: Array<{k: string, v: any}>) => Record<string, any>} */
 export const _mapToRecord = map =>
-  map.reduce((r, {k, v}) => {
+  map.reduce((r, { k, v }) => {
     r[k] = v
     return r
   }, emptyRecord())
diff --git a/src/Puppeteer.FFI.purs b/src/Puppeteer.FFI.purs
index cc86638..9675bcc 100644
--- a/src/Puppeteer.FFI.purs
+++ b/src/Puppeteer.FFI.purs
@@ -15,14 +15,14 @@ import Foreign (Foreign)
 import Simple.JSON (class WriteForeign)
 
 foreign import mergeRecords :: Array Foreign -> Foreign
-foreign import _mapToRecord :: forall a. Array {k :: String, v :: a} -> Foreign
+foreign import _mapToRecord :: forall a. Array { k :: String, v :: a } -> Foreign
 foreign import _maybeToUndefined :: forall a. (Maybe a -> Nullable a) -> Maybe a -> Foreign
 
 makeMap :: forall k v. Ord k => Array { k :: k, v :: v } -> Map k v
 makeMap = Map.fromFoldable <<< map (\{ k, v } -> Tuple k v)
 
 mapToRecord :: forall a. WriteForeign a => Map String a -> Foreign
-mapToRecord = _mapToRecord <<< foldlWithIndex (\k a v -> Array.cons {k, v} a) []
+mapToRecord = _mapToRecord <<< foldlWithIndex (\k a v -> Array.cons { k, v } a) []
 
 maybeToUndefined :: forall a. WriteForeign a => Maybe a -> Foreign
 maybeToUndefined = _maybeToUndefined Nullable.toNullable
diff --git a/src/Puppeteer.Handle.HTML.purs b/src/Puppeteer.Handle.HTML.purs
index 0b45c3a..ce5ecdd 100644
--- a/src/Puppeteer.Handle.HTML.purs
+++ b/src/Puppeteer.Handle.HTML.purs
@@ -81,35 +81,37 @@ offsetHeight :: forall a. IsElement a => Handle a -> Aff (Array Number)
 offsetHeight = Eval.unsafeRunJs0 "e => e.offsetHeight"
 
 attrs :: forall a. IsElement a => Handle a -> Aff (Map String String)
-attrs = let
-  js = String.joinWith "\n"
-        [ "e => Array.from(e.attributes)"
-        , "          .reduce("
-        , "            (m, a) => [...m, {k: a.name, v: a.value}],"
-        , "            [],"
-        , "          )"
-        , "          .filter(({k}) => k)"
-        ]
+attrs =
+  let
+    js = String.joinWith "\n"
+      [ "e => Array.from(e.attributes)"
+      , "          .reduce("
+      , "            (m, a) => [...m, {k: a.name, v: a.value}],"
+      , "            [],"
+      , "          )"
+      , "          .filter(({k}) => k)"
+      ]
   in
-    map FFI.makeMap <<< Eval.unsafeRunJs0 @(Array {k :: String, v :: String}) js
+    map FFI.makeMap <<< Eval.unsafeRunJs0 @(Array { k :: String, v :: String }) js
 
 computedStyle :: forall a. IsElement a => Handle a -> Aff (Map String String)
-computedStyle = let
+computedStyle =
+  let
     js = String.joinWith "\n"
-           [ "e => {"
-           , "  const s = window.getComputedStyle(e)"
-           , "  const a = []"
-           , "  for (let i = 0; i < s.length; i++) {"
-           , "    const k = s.item(i)"
-           , "    const v = s.getPropertyValue(k)"
-           , "    a.push({k, v})"
-           , "  }"
-           , ""
-           , "  return a"
-           , "}"
-           ]
+      [ "e => {"
+      , "  const s = window.getComputedStyle(e)"
+      , "  const a = []"
+      , "  for (let i = 0; i < s.length; i++) {"
+      , "    const k = s.item(i)"
+      , "    const v = s.getPropertyValue(k)"
+      , "    a.push({k, v})"
+      , "  }"
+      , ""
+      , "  return a"
+      , "}"
+      ]
   in
-    map FFI.makeMap <<< Eval.unsafeRunJs0 @(Array {k :: String, v :: String}) js
+    map FFI.makeMap <<< Eval.unsafeRunJs0 @(Array { k :: String, v :: String }) js
 
 value :: Handle HTML.HTMLInputElement -> Aff String
 value = Eval.unsafeRunJs0 "e => e.value"
diff --git a/src/Puppeteer.Handle.js b/src/Puppeteer.Handle.js
index 364c95c..4366a2e 100644
--- a/src/Puppeteer.Handle.js
+++ b/src/Puppeteer.Handle.js
@@ -4,14 +4,17 @@ import { ElementHandle } from 'puppeteer'
 import { JSHandle } from 'puppeteer'
 
 /** @type {<T>(_: { remoteObject: (_0: string) => T, primitive: (_0: unknown) => T }) => (_: JSHandle<unknown>) => () => T} */
-export const _id = ({remoteObject, primitive}) => h => () => {
-  const oid = h.remoteObject().objectId
-  if (oid) {
-    return remoteObject(oid)
-  } else {
-    return primitive(h.remoteObject().value)
+export const _id =
+  ({ remoteObject, primitive }) =>
+  h =>
+  () => {
+    const oid = h.remoteObject().objectId
+    if (oid) {
+      return remoteObject(oid)
+    } else {
+      return primitive(h.remoteObject().value)
+    }
   }
-}
 
 /** @type {(_: string) => (_: ElementHandle<HTMLElement>) => Promise<Array<ElementHandle<Node>>>} */
 export const _find = s => h => h.$$(s)
diff --git a/src/Puppeteer.Handle.purs b/src/Puppeteer.Handle.purs
index 097dbeb..75ba53d 100644
--- a/src/Puppeteer.Handle.purs
+++ b/src/Puppeteer.Handle.purs
@@ -60,7 +60,7 @@ import Web.HTML (HTMLElement)
 import Web.HTML as HTML
 
 id :: forall a. Handle a -> Effect HandleId
-id = _id {remoteObject: HandleObject, primitive: HandlePrimitive}
+id = _id { remoteObject: HandleObject, primitive: HandlePrimitive }
 
 data HandleId
   = HandleObject String
diff --git a/src/Puppeteer.Page.Event.ConsoleMessage.purs b/src/Puppeteer.Page.Event.ConsoleMessage.purs
index ef7f8f2..707dd90 100644
--- a/src/Puppeteer.Page.Event.ConsoleMessage.purs
+++ b/src/Puppeteer.Page.Event.ConsoleMessage.purs
@@ -14,7 +14,9 @@ import Prelude
 import Control.Monad.Except (runExcept)
 import Data.Array as Array
 import Data.Either (hush)
+import Data.Generic.Rep (class Generic)
 import Data.Maybe (Maybe)
+import Data.Show.Generic (genericShow)
 import Foreign (Foreign, unsafeFromForeign)
 import Puppeteer.Base (Handle)
 import Puppeteer.FFI as FFI
@@ -54,6 +56,10 @@ data MessageType
   | TimeEnd
   | Verbose
 
+derive instance eqMessageType :: Eq MessageType
+derive instance genericMessageType :: Generic MessageType _
+instance showMessageType :: Show MessageType where show = genericShow
+
 messageTypeOfString :: String -> MessageType
 messageTypeOfString "debug" = Debug
 messageTypeOfString "info" = Info
diff --git a/src/Puppeteer.Page.Event.purs b/src/Puppeteer.Page.Event.purs
index 3e0c21e..abd7ea1 100644
--- a/src/Puppeteer.Page.Event.purs
+++ b/src/Puppeteer.Page.Event.purs
@@ -41,7 +41,8 @@ import Puppeteer.Page.Event.Dialog (Dialog)
 import Simple.JSON (class ReadForeign, readImpl)
 
 connectPageConsole :: Page -> Aff Unit
-connectPageConsole p = let
+connectPageConsole p =
+  let
     onmsg m = do
       title <- Page.title p
       let t = ConsoleMessage.messageType m
diff --git a/src/Puppeteer.Page.purs b/src/Puppeteer.Page.purs
index a9b8c0e..447f8b6 100644
--- a/src/Puppeteer.Page.purs
+++ b/src/Puppeteer.Page.purs
@@ -138,7 +138,7 @@ close = Promise.toAff <<< _close
 content :: Page -> Aff String
 content = Promise.toAff <<< _content
 
-setContent :: String  -> LifecycleEvent -> Page -> Aff Unit
+setContent :: String -> LifecycleEvent -> Page -> Aff Unit
 setContent s ev = Promise.toAff <<< _setContent s (prepareLifecycleEvent ev)
 
 setViewport :: Viewport -> Page -> Aff Unit
diff --git a/test/Puppeteer.Page.Event.Spec.purs b/test/Puppeteer.Page.Event.Spec.purs
new file mode 100644
index 0000000..9423c89
--- /dev/null
+++ b/test/Puppeteer.Page.Event.Spec.purs
@@ -0,0 +1,78 @@
+module Puppeteer.Page.Event.Spec where
+
+import Prelude
+
+import Control.Monad.Error.Class (liftMaybe)
+import Control.Monad.Rec.Class (untilJust)
+import Control.Monad.ST.Class (liftST)
+import Control.Monad.ST.Global as ST
+import Control.Monad.ST.Ref as ST.Ref
+import Data.Array as Array
+import Data.Array.NonEmpty as NonEmptyArray
+import Data.Map as Map
+import Data.Maybe (Maybe(..))
+import Data.Newtype (wrap)
+import Data.Time.Duration (Milliseconds(..))
+import Effect (Effect)
+import Effect.Aff (Aff, forkAff, joinFiber, makeAff)
+import Effect.Class (liftEffect)
+import Effect.Exception (error)
+import Effect.Exception as Error
+import Puppeteer as Pup
+import Puppeteer.Base (timeoutThrow)
+import Puppeteer.Handle as Pup.Handle
+import Puppeteer.Handle.HTML as Pup.Handle.HTML
+import Puppeteer.Keyboard as Pup.Keyboard
+import Puppeteer.Page as Pup.Page
+import Puppeteer.Page.Event (connectPageConsole)
+import Puppeteer.Page.Event as Pup.Page.Event
+import Puppeteer.Page.Event.ConsoleMessage as ConsoleMessage
+import Puppeteer.Page.WaitFor as Pup.Page.WaitFor
+import Test.Spec (SpecT, afterAll, beforeAll, describe)
+import Test.Spec.Assertions (shouldEqual)
+import Test.Util (failOnPageError, test)
+
+scriptError :: String
+scriptError = "throw new Error('eek!')"
+
+scriptLog :: String
+scriptLog = "console.log('beak')"
+
+listenIntoSTArray :: forall e ed. Pup.Page.Event.Event e ed => e -> Pup.Page -> Aff ({ st :: ST.Ref.STRef ST.Global (Array ed), cleanup :: Aff Unit })
+listenIntoSTArray e p = do
+  st <- liftST $ ST.Ref.new []
+  let
+    handle ed = do
+      eds <- liftST $ ST.Ref.read st
+      _ <- liftST $ ST.Ref.write (eds <> [ ed ]) st
+      pure unit
+  t <- Pup.Page.Event.listen e handle p
+  pure { st, cleanup: Pup.closeContext t }
+
+spec :: SpecT Aff Unit Effect Unit
+spec =
+  beforeAll (Pup.Page.new =<< Pup.launch_ =<< Pup.puppeteer unit)
+    $ afterAll Pup.Page.close
+    $ describe "Page" do
+        test "listen, PageError" \p -> do
+          { st: errsST, cleanup } <- listenIntoSTArray Pup.Page.Event.PageError p
+          _ <- Pup.Page.addScriptTag (Pup.Page.AddScriptInline Pup.Page.Script scriptError) p
+          err <- timeoutThrow (wrap 1000.0)
+            $ untilJust do
+                errs <- liftST $ ST.Ref.read errsST
+                pure $ Array.head errs
+          Error.message err `shouldEqual` "eek!"
+          cleanup
+
+        test "once" \p -> do
+          errF <- forkAff $ Pup.Page.Event.once Pup.Page.Event.PageError p
+          _ <- Pup.Page.addScriptTag (Pup.Page.AddScriptInline Pup.Page.Script scriptError) p
+          err <- joinFiber errF
+          Error.message err `shouldEqual` "eek!"
+
+        test "Console" \p -> do
+          logF <- forkAff $ Pup.Page.Event.once Pup.Page.Event.Console p
+          _ <- Pup.Page.addScriptTag (Pup.Page.AddScriptInline Pup.Page.Script scriptLog) p
+          log <- joinFiber logF
+          ConsoleMessage.text log `shouldEqual` "beak"
+          ConsoleMessage.messageType log `shouldEqual` ConsoleMessage.Log
diff --git a/test/Puppeteer.Page.Spec.purs b/test/Puppeteer.Page.Spec.purs
index 39e5b38..9915f22 100644
--- a/test/Puppeteer.Page.Spec.purs
+++ b/test/Puppeteer.Page.Spec.purs
@@ -105,13 +105,15 @@ spec = beforeAll (Pup.launch_ =<< Pup.puppeteer unit)
 
       test "setViewport, viewport" \b -> do
         p <- Pup.Page.new b
-        let vp = { deviceScaleFactor: Nothing
-                 , hasTouch: Nothing
-                 , height: 1200
-                 , width: 800
-                 , isLandscape: Nothing
-                 , isMobile: Nothing
-                 }
+        let
+          vp =
+            { deviceScaleFactor: Nothing
+            , hasTouch: Nothing
+            , height: 1200
+            , width: 800
+            , isLandscape: Nothing
+            , isMobile: Nothing
+            }
 
         Pup.Page.setViewport vp p
         vp' <- liftMaybe (error "no viewport!") $ Pup.Page.viewport p
diff --git a/test/Test.Main.purs b/test/Test.Main.purs
index c9e01fb..e88408b 100644
--- a/test/Test.Main.purs
+++ b/test/Test.Main.purs
@@ -18,6 +18,7 @@ import Node.Process as Process
 import Node.Stream as Writable
 import Puppeteer.Browser.Spec as Spec.Browser
 import Puppeteer.Page.Spec as Spec.Page
+import Puppeteer.Page.Event.Spec as Spec.Page.Event
 import Puppeteer.Spec as Spec
 import Test.Spec (SpecT)
 import Test.Spec.Config (defaultConfig)
@@ -32,6 +33,7 @@ specs = do
   Spec.spec
   Spec.Browser.spec
   Spec.Page.spec
+  Spec.Page.Event.spec
 
 main :: Effect Unit
 main = launchAff_ do
diff --git a/test/Test.Util.purs b/test/Test.Util.purs
index 6f2a8ba..ef8de29 100644
--- a/test/Test.Util.purs
+++ b/test/Test.Util.purs
@@ -27,7 +27,8 @@ testA :: forall m t arg g. MonadAff g => Monad m => Example t arg Aff => String
 testA = test_ liftAff
 
 failOnPageError :: forall a. Pup.Page -> Aff a -> Aff a
-failOnPageError p a = let
+failOnPageError p a =
+  let
     ok = parallel $ try a
     err = parallel $ Left <$> Pup.Page.Event.once Pup.Page.Event.PageError p
   in