From 469dc31765e0a8bb915437346ea92e09b515a8a6 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Sun, 6 Dec 2020 02:57:57 +0900
Subject: [PATCH] jsutil: Reduce allocating Uint8Array on go2cpp

Updates #1426
---
 internal/jsutil/buf_js.go   | 14 +++++++++-----
 internal/jsutil/slice_js.go |  2 +-
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/internal/jsutil/buf_js.go b/internal/jsutil/buf_js.go
index f4273db5e..a858beb3b 100644
--- a/internal/jsutil/buf_js.go
+++ b/internal/jsutil/buf_js.go
@@ -28,8 +28,6 @@ var isTypedArrayWritable = js.Global().Get("go2cpp").Truthy()
 // To avoid often allocating ArrayBuffer, reuse the buffer whenever possible.
 var temporaryBuffer = js.Global().Get("ArrayBuffer").New(16)
 
-var uint8ArrayObj js.Value
-
 func TemporaryUint8Array(byteLength int) js.Value {
 	if bufl := temporaryBuffer.Get("byteLength").Int(); bufl < byteLength {
 		for bufl < byteLength {
@@ -37,14 +35,20 @@ func TemporaryUint8Array(byteLength int) js.Value {
 		}
 		temporaryBuffer = js.Global().Get("ArrayBuffer").New(bufl)
 	}
+	return uint8Array(temporaryBuffer, 0, byteLength)
+}
+
+var uint8ArrayObj js.Value
+
+func uint8Array(buffer js.Value, byteOffset, byteLength int) js.Value {
 	if isTypedArrayWritable {
 		if uint8ArrayObj.IsUndefined() {
 			uint8ArrayObj = js.Global().Get("Uint8Array").New()
 		}
-		uint8ArrayObj.Set("buffer", temporaryBuffer)
-		uint8ArrayObj.Set("byteOffset", 0)
+		uint8ArrayObj.Set("buffer", buffer)
+		uint8ArrayObj.Set("byteOffset", byteOffset)
 		uint8ArrayObj.Set("byteLength", byteLength)
 		return uint8ArrayObj
 	}
-	return js.Global().Get("Uint8Array").New(temporaryBuffer, 0, byteLength)
+	return js.Global().Get("Uint8Array").New(buffer, byteOffset, byteLength)
 }
diff --git a/internal/jsutil/slice_js.go b/internal/jsutil/slice_js.go
index a495df15f..d4ace466c 100644
--- a/internal/jsutil/slice_js.go
+++ b/internal/jsutil/slice_js.go
@@ -95,7 +95,7 @@ func CopySliceToJS(dst js.Value, src interface{}) {
 	case []uint8:
 		js.CopyBytesToJS(dst, s)
 	case []int8, []int16, []int32, []uint16, []uint32, []float32, []float64:
-		a := js.Global().Get("Uint8Array").New(dst.Get("buffer"), dst.Get("byteOffset"), dst.Get("byteLength"))
+		a := uint8Array(dst.Get("buffer"), dst.Get("byteOffset").Int(), dst.Get("byteLength").Int())
 		js.CopyBytesToJS(a, sliceToByteSlice(s))
 	default:
 		panic(fmt.Sprintf("jsutil: unexpected value at CopySliceToJS: %T", s))