From 3b2fe3cd33b74166c3debec9826826f2b5a54fd9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B8rn=20Erik=20Pedersen?=
 <bjorn.erik.pedersen@gmail.com>
Date: Tue, 3 Nov 2020 09:05:09 +0100
Subject: js: Add avoidTDZ option

Fixes #7865
---
 resources/resource_transformers/js/options.go      | 12 ++++++++++++
 resources/resource_transformers/js/options_test.go |  8 +++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

(limited to 'resources/resource_transformers')

diff --git a/resources/resource_transformers/js/options.go b/resources/resource_transformers/js/options.go
index 5e74982d3..84a6c1a78 100644
--- a/resources/resource_transformers/js/options.go
+++ b/resources/resource_transformers/js/options.go
@@ -70,6 +70,16 @@ type Options struct {
 	// What to use instead of React.Fragment.
 	JSXFragment string
 
+	// There is/was a bug in WebKit with severe performance issue with the tracking
+	// of TDZ checks in JavaScriptCore.
+	//
+	// Enabling this flag removes the TDZ and `const` assignment checks and
+	// may improve performance of larger JS codebases until the WebKit fix
+	// is in widespread use.
+	//
+	// See https://bugs.webkit.org/show_bug.cgi?id=199866
+	AvoidTDZ bool
+
 	mediaType  media.Type
 	outDir     string
 	contents   string
@@ -339,6 +349,8 @@ func toBuildOptions(opts Options) (buildOptions api.BuildOptions, err error) {
 		JSXFactory:  opts.JSXFactory,
 		JSXFragment: opts.JSXFragment,
 
+		AvoidTDZ: opts.AvoidTDZ,
+
 		Tsconfig: opts.tsConfig,
 
 		Stdin: &api.StdinOptions{
diff --git a/resources/resource_transformers/js/options_test.go b/resources/resource_transformers/js/options_test.go
index 89d362ab9..abc8091a9 100644
--- a/resources/resource_transformers/js/options_test.go
+++ b/resources/resource_transformers/js/options_test.go
@@ -54,7 +54,12 @@ func TestToBuildOptions(t *testing.T) {
 	})
 
 	opts, err = toBuildOptions(Options{
-		Target: "es2018", Format: "cjs", Minify: true, mediaType: media.JavascriptType})
+		Target:    "es2018",
+		Format:    "cjs",
+		Minify:    true,
+		mediaType: media.JavascriptType,
+		AvoidTDZ:  true,
+	})
 	c.Assert(err, qt.IsNil)
 	c.Assert(opts, qt.DeepEquals, api.BuildOptions{
 		Bundle:            true,
@@ -63,6 +68,7 @@ func TestToBuildOptions(t *testing.T) {
 		MinifyIdentifiers: true,
 		MinifySyntax:      true,
 		MinifyWhitespace:  true,
+		AvoidTDZ:          true,
 		Stdin: &api.StdinOptions{
 			Loader: api.LoaderJS,
 		},
-- 
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