show welcome page as previous page for root pages

Author: chargome

src/docTree.spec.ts

@@ -270,7 +270,7 @@ describe('docTree', () => {
       expect(getPreviousNode(xA)).toBe(xB);
     });
 
-    test('should not return siblings for root platform or guide paths', () => {
+    test('should return root as previous page for root platform or guide paths', () => {
       const platforms = createNode('platforms', 'Platforms');
       const js = createNode('platforms/javascript', 'JavaScript');
       const python = createNode('platforms/python', 'Python');
@@ -286,10 +286,10 @@ describe('docTree', () => {
         child.parent = js;
       });
 
-      expect(getPreviousNode(js)).toBe(undefined);
-      expect(getPreviousNode(python)).toBe(undefined);
-      expect(getPreviousNode(nextjs)).toBe(undefined);
-      expect(getPreviousNode(angular)).toBe(undefined);
+      expect(getPreviousNode(js)).toBe('root');
+      expect(getPreviousNode(python)).toBe('root');
+      expect(getPreviousNode(nextjs)).toBe('root');
+      expect(getPreviousNode(angular)).toBe('root');
     });
 
     test('should not return /platforms as previous page', () => {

src/docTree.ts

@@ -185,9 +185,10 @@ export const getNextNode = (node: DocNode): DocNode | undefined => {
  * Returns the previous node in the tree, which is either the last child of the parent,
  * the previous sibling, or the previous sibling of a parent node.
  */
-export const getPreviousNode = (node: DocNode): DocNode | undefined => {
+export const getPreviousNode = (node: DocNode): DocNode | undefined | 'root' => {
+  // in this special case, calculating the root node is unnecessary so we return a string instead
   if (isRootPlatformPath(node.path) || isRootGuidePath(node.path)) {
-    return undefined;
+    return 'root';
   }
 
   const previousSibling = getPreviousSiblingNode(node);