From eb75f8c8cc2316fbf68a4fa26841e77292c71f3c Mon Sep 17 00:00:00 2001
From: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>
Date: Wed, 19 Aug 2020 22:30:46 +0200
Subject: [PATCH] fix(client): ensure presetEnv is loaded (#39431)

Prior to this, if a user first loaded a React challenge and then
navigated to a JS challenge, they would see
TypeError: Cannot read property 'presets' of undefined
in the console and be unable to run tests or evaluate code until they
reloaded the page.
---
 .../src/templates/Challenges/rechallenge/transformers.js | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/client/src/templates/Challenges/rechallenge/transformers.js b/client/src/templates/Challenges/rechallenge/transformers.js
index 0dc65c2a0f..061e160c61 100644
--- a/client/src/templates/Challenges/rechallenge/transformers.js
+++ b/client/src/templates/Challenges/rechallenge/transformers.js
@@ -59,11 +59,12 @@ async function loadBabel() {
 }
 
 async function loadPresetEnv() {
-  if (presetEnv) return;
+  if (babelOptionsJSBase && babelOptionsJSBase.presets) return;
   /* eslint-disable no-inline-comments */
-  presetEnv = await import(
-    /* webpackChunkName: "@babel/preset-env" */ '@babel/preset-env'
-  );
+  if (!presetEnv)
+    presetEnv = await import(
+      /* webpackChunkName: "@babel/preset-env" */ '@babel/preset-env'
+    );
   /* eslint-enable no-inline-comments */
 
   babelOptionsJSBase = {