diff --git a/.devcontainer/post-create.sh b/.devcontainer/post-create.sh
index d27e4297..1aff43ad 100755
--- a/.devcontainer/post-create.sh
+++ b/.devcontainer/post-create.sh
@@ -11,3 +11,9 @@ bundle install
 
 # Set up the databases: create the schema, and load in some default data.
 bin/rails db:schema:load db:seed
+
+# Install the app's JS dependencies.
+yarn install
+
+# Run a first-time build of the app's JS, in development mode.
+yarn build:dev
diff --git a/package.json b/package.json
index 98488824..f341db16 100644
--- a/package.json
+++ b/package.json
@@ -31,6 +31,7 @@
   },
   "scripts": {
     "build": "esbuild app/javascript/*.* --bundle --sourcemap --outdir=app/assets/builds --public-path=/assets --asset-names=[name]-[hash].digested --loader:.js=jsx --loader:.png=file --loader:.svg=file --loader:.min.js=text",
-    "dev": "yarn build --watch --public-path=/dev-assets"
+    "build:dev": "yarn build --public-path=/dev-assets",
+    "dev": "yarn build:dev --watch"
   }
 }