build: cache javascript downloads

.repo/build

@@ -49,6 +49,14 @@ for package in "${PACKAGES[@]}"; do
       EXTRA_ARGS+=(--bind-rw /var/cache/dartlang:/build/.pub-cache)
     fi
 
+    # javascript - npm/yarn/pkg
+    if grep -q "depends = npm\|yarn\|nodejs" <<<"$makepkg_output"; then
+      EXTRA_ARGS+=(
+        --bind-rw /var/cache/javascript/npm:/build/.npm
+        --bind-rw /var/cache/javascript/pkg-cache:/build/.pkg-cache
+      )
+    fi
+
     # build signed package in chroot & add to local repo
     aur build \
       --chroot \