Upgrade to Babel 7

Also, update to webpack 4 and add support for dynamic import() and
import.meta in ?module mode.

Fixes #108
Fixes #151

modules/plugins/unpkgRewrite.js

@@ -5,40 +5,85 @@ const origin = require("../serverConfig").origin;
 
 const bareIdentifierFormat = /^((?:@[^/]+\/)?[^/]+)(\/.*)?$/;
 
+function isValidURL(value) {
+  return URL.parseURL(value) != null;
+}
+
+function isProbablyURLWithoutProtocol(value) {
+  return value.substr(0, 2) === "//";
+}
+
+function isAbsoluteURL(value) {
+  return isValidURL(value) || isProbablyURLWithoutProtocol(value);
+}
+
+function isBareIdentifier(value) {
+  return value.charAt(0) !== "." && value.charAt(0) !== "/";
+}
+
+function rewriteValue(/* StringLiteral */ node, dependencies) {
+  if (isAbsoluteURL(node.value)) {
+    return;
+  }
+
+  if (isBareIdentifier(node.value)) {
+    // "bare" identifier
+    const match = bareIdentifierFormat.exec(node.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";
+
+    node.value = `${origin}/${packageName}@${version}${file}?module`;
+  } else {
+    // local path
+    node.value = `${node.value}?module`;
+  }
+}
+
 function unpkgRewrite(dependencies = {}) {
   return {
-    inherits: require("babel-plugin-syntax-export-extensions"),
+    manipulateOptions(opts, parserOpts) {
+      parserOpts.plugins.push(
+        "dynamicImport",
+        "exportDefaultFrom",
+        "exportNamespaceFrom",
+        "importMeta"
+      );
+    },
 
     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 = `${path.node.source.value}?module`;
-        } else {
-          // "bare" identifier
-          const match = bareIdentifierFormat.exec(path.node.source.value);
-          const packageName = match[1];
-          const file = match[2] || "";
-
-          warning(
-            dependencies[packageName],
-            'Missing version info for package "%s" in dependencies; falling back to "latest"',
-            packageName
-          );
-
-          const version = dependencies[packageName] || "latest";
-          const url = `${origin}/${packageName}@${version}${file}?module`;
-
-          path.node.source.value = url;
+      CallExpression(path) {
+        if (path.node.callee.type !== "Import") {
+          // Some other function call, not import();
+          return;
         }
+
+        rewriteValue(path.node.arguments[0], dependencies);
+      },
+      ExportAllDeclaration(path) {
+        return rewriteValue(path.node.source, dependencies);
+      },
+      ExportNamedDeclaration(path) {
+        if (!path.node.source) {
+          // This export has no "source", so it's probably
+          // a local variable or function, e.g.
+          // export { varName }
+          // export const constName = ...
+          // export function funcName() {}
+          return;
+        }
+
+        rewriteValue(path.node.source, dependencies);
+      },
+      ImportDeclaration(path) {
+        return rewriteValue(path.node.source, dependencies);
       }
     }
   };