Patching prepareImport before loading script modules. Resolves #2024.

src/system.js

@@ -1,6 +1,6 @@
+import './features/import-map.js';
 import './features/script-load.js';
 import './features/worker-load.js';
 import './extras/global.js';
 import './extras/module-types.js';
-import './features/import-map.js';
 import './features/registry.js';

test/browser/core.js

@@ -191,4 +191,10 @@ suite('SystemJS Standard Tests', function() {
     assert.ok(System.has(resolved));
     assert.equal(System.get(resolved).hello, 'there');
   });
+
+  test('should load <script type=systemjs-module> that is in the dom before systemjs is loaded', function () {
+    const resolved = System.resolve('/test/fixtures/browser/systemjs-module-early.js');
+    assert.ok(System.has(resolved));
+    assert.equal(System.get(resolved).hi, 'bye');
+  })
 });

test/fixtures/browser/systemjs-module-early.js

@@ -0,0 +1,7 @@
+System.register([], function(_export) {
+  return {
+    execute: function () {
+      _export('hi', 'bye');
+    }
+  };
+});

test/test.html

@@ -19,6 +19,7 @@
 	<script src="../node_modules/mocha/mocha.js"></script>
 
 	<script type="systemjs-importmap" src="fixtures/browser/importmap.json"></script>
+	<script type="systemjs-module" src="/test/fixtures/browser/systemjs-module-early.js"></script>
 	<script src="../dist/system.js"></script>
 	<script type="systemjs-module" src="/test/fixtures/browser/systemjs-module-script.js"></script>
 	<script type="systemjs-module" src="import:/test/fixtures/browser/systemjs-module-script2.js"></script>