fix(base): Ensure this.root_ is available within getDefaultFoundation…

…() (#279)

Fixes #242

packages/mdc-base/component.js

@@ -25,10 +25,12 @@ export default class MDCComponent {
     return new MDCComponent(root, new MDCFoundation());
   }
 
-  constructor(root, foundation = this.getDefaultFoundation(), ...args) {
+  constructor(root, foundation = undefined, ...args) {
     this.root_ = root;
     this.initialize(...args);
-    this.foundation_ = foundation;
+    // Note that we initialize foundation here and not within the constructor's default param so that
+    // this.root_ is defined and can be used within the foundation class.
+    this.foundation_ = foundation === undefined ? this.getDefaultFoundation() : foundation;
     this.foundation_.init();
     this.initialSyncWithDOM();
   }

test/unit/mdc-base/component.test.js

@@ -33,6 +33,7 @@ class FakeComponent extends MDCComponent {
     return td.object({
       isDefaultFoundation: true,
       init: () => {},
+      rootElementAtTimeOfCall: this.root_,
     });
   }
 
@@ -163,3 +164,10 @@ test('#emit dispatches a custom event with the supplied data', (t) => {
   t.deepEqual(evt.detail, data);
   t.end();
 });
+
+test('(regression) ensures that this.root_ is available for use within getDefaultFoundation()', (t) => {
+  const root = document.createElement('div');
+  const f = new FakeComponent(root);
+  t.equal(f.foundation.rootElementAtTimeOfCall, root);
+  t.end();
+});