From 4113c1d6741d802292f424711a0d114a5f332a9a Mon Sep 17 00:00:00 2001
From: Grex <grxy@users.noreply.github.com>
Date: Mon, 20 Dec 2021 01:27:05 -0700
Subject: [PATCH] perf: only register ts-node once when loading TS config files
 (#12160)

---
 CHANGELOG.md                                            | 2 ++
 packages/jest-config/src/readConfigFileAndSetRootDir.ts | 6 +++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9ebe7e025867..de59fb365eec 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,8 @@
 
 ### Performance
 
+- `jest-config` perf: only register ts-node once when loading TS config files ([#12160](https://github.com/facebook/jest/pull/12160))
+
 ## 27.4.5
 
 ### Fixes
diff --git a/packages/jest-config/src/readConfigFileAndSetRootDir.ts b/packages/jest-config/src/readConfigFileAndSetRootDir.ts
index 09a2aaa8c896..6bf555c77911 100644
--- a/packages/jest-config/src/readConfigFileAndSetRootDir.ts
+++ b/packages/jest-config/src/readConfigFileAndSetRootDir.ts
@@ -79,15 +79,15 @@ export default async function readConfigFileAndSetRootDir(
   return configObject;
 }
 
+let registerer: Service;
+
 // Load the TypeScript configuration
 const loadTSConfigFile = async (
   configPath: Config.Path,
 ): Promise<Config.InitialOptions> => {
-  let registerer: Service;
-
   // Register TypeScript compiler instance
   try {
-    registerer = require('ts-node').register({
+    registerer ||= require('ts-node').register({
       compilerOptions: {
         module: 'CommonJS',
       },