Better dev server integration

server/utils/unpkgRewriteBabelPlugin.js

@@ -0,0 +1,44 @@
+const URL = require("whatwg-url")
+const warning = require("warning")
+
+const BareIdentifierFormat = /^((?:@[^\/]+\/)?[^\/]+)(\/.*)?$/
+
+function unpkgRewriteBabelPlugin(dependencies = {}) {
+  return {
+    inherits: require("babel-plugin-syntax-export-extensions"),
+
+    visitor: {
+      "ImportDeclaration|ExportNamedDeclaration|ExportAllDeclaration"(path) {
+        if (!path.node.source) return // probably a variable declaration
+
+        if (
+          URL.parseURL(path.node.source.value) != null ||
+          path.node.source.value.substr(0, 2) === "//"
+        )
+          return // valid URL or URL w/o protocol, leave it alone
+
+        if ([".", "/"].indexOf(path.node.source.value.charAt(0)) >= 0) {
+          // local path
+          path.node.source.value = `${path.node.source.value}?module`
+        } else {
+          // "bare" identifier
+          const match = BareIdentifierFormat.exec(path.node.source.value)
+          const packageName = match[1]
+          const file = match[2] || ""
+
+          warning(
+            dependencies[packageName],
+            'Missing version info for package "%s" in dependencies; falling back to "latest"',
+            packageName
+          )
+
+          const version = dependencies[packageName] || "latest"
+
+          path.node.source.value = `https://unpkg.com/${packageName}@${version}${file}?module`
+        }
+      }
+    }
+  }
+}
+
+module.exports = unpkgRewriteBabelPlugin