Fall back to Date.now() when performance is unavailable (#1627)

Author: nanofuxion

ffi/ghc/Miso/DSL/FFI.hs

@@ -119,6 +119,10 @@ freeJSVal_ffi _ = pure ()
 requestAnimationFrame :: JSVal -> IO Int
 requestAnimationFrame = undefined
 -----------------------------------------------------------------------------
+-- | High-resolution timestamp where one exists, wall clock where it does not.
+now_ffi :: IO Double
+now_ffi = undefined
+-----------------------------------------------------------------------------
 -- | Cancels a frame previously scheduled with 'requestAnimationFrame'.
 --
 -- @since 1.13.0.0

ffi/js/Miso/DSL/FFI.hs

@@ -9,6 +9,7 @@ module Miso.DSL.FFI
   ( -- ** Types
     JSVal
   , JSString
+  , now_ffi
     -- ** Serialization FFI
     -- *** ToJSVal
   , toJSVal_Char
@@ -467,3 +468,15 @@ foreign import javascript unsafe
 #endif
   toString_Word :: Word -> JSString
 -----------------------------------------------------------------------------
+-- | High-resolution timestamp where one exists, wall clock where it does not.
+--
+-- @performance@ is absent on Lynx's background-thread realm, so this cannot be
+-- a bare @performance.now()@; see 'Miso.FFI.Internal.now'.
+foreign import javascript unsafe
+#if GHCJS_NEW
+  "(() => (typeof performance !== 'undefined' && performance && typeof performance.now === 'function') ? performance.now() : Date.now())"
+#else
+  "$r = (typeof performance !== 'undefined' && performance && typeof performance.now === 'function') ? performance.now() : Date.now();"
+#endif
+  now_ffi :: IO Double
+-----------------------------------------------------------------------------

ffi/wasm/Miso/DSL/FFI.hs

@@ -12,6 +12,7 @@ module Miso.DSL.FFI
   ( -- ** Types
     JSVal
   , JSString (..)
+  , now_ffi
     -- ** Serialization FFI
     -- *** ToJSVal
   , toJSVal_Char
@@ -447,6 +448,14 @@ foreign import javascript unsafe
   return requestAnimationFrame($1);
   """ requestAnimationFrame :: JSVal -> IO Int
 -----------------------------------------------------------------------------
+-- | High-resolution timestamp where one exists, wall clock where it does not.
+foreign import javascript unsafe
+  """
+  return (typeof performance !== 'undefined' && performance && typeof performance.now === 'function')
+    ? performance.now()
+    : Date.now();
+  """ now_ffi :: IO Double
+-----------------------------------------------------------------------------
 foreign import javascript unsafe
   """
   return cancelAnimationFrame($1);

src/Miso/DSL.hs

@@ -143,6 +143,7 @@ module Miso.DSL
   , setProp
   , getProp
   , eval
+  , now_ffi
   , requestAnimationFrame
   , cancelAnimationFrame
   , freeFunction

src/Miso/FFI/Internal.hs

@@ -376,9 +376,15 @@ windowInnerWidth =
 -- | Retrieve high resolution time stamp
 --
 -- See <https://developer.mozilla.org/en-US/docs/Web/API/Performance/now>
+-- Lynx's *background* thread realm has no @performance@ global at all - only
+-- the main thread does - so the obvious @performance.now()@ throws
+-- @cannot read property 'now' of undefined@ there. Everything that timestamps
+-- from the BTS goes through here, including gesture handling like
+-- double-tap detection, so that throw took real features down rather than
+-- merely losing precision. Falls back to @Date.now()@, which every realm has.
 now :: IO Double
 {-# INLINABLE now #-}
-now = fromJSValUnchecked =<< (jsg "performance" # "now" $ ())
+now = now_ffi
 -----------------------------------------------------------------------------
 -- | Outputs a message to the web console
 --