idb: make unique cursor work

packages/idb-bridge/src/MemoryBackend.test.ts

@@ -188,6 +188,32 @@ test("Spec: Example 1 Part 3", async t => {
   t.is(cursor.value.author, "Fred");
   cursor.continue();
 
+  await promiseFromRequest(request5);
+  cursor = request5.result;
+  t.is(cursor.value.author, "Fred");
+  cursor.continue();
+
+  await promiseFromRequest(request5);
+  cursor = request5.result;
+  t.is(cursor, null);
+
+  const request6 = index5.openCursor(null, "nextunique");
+
+  await promiseFromRequest(request6);
+  cursor = request6.result;
+  t.is(cursor.value.author, "Barney");
+  cursor.continue();
+
+  await promiseFromRequest(request6);
+  cursor = request6.result;
+  t.is(cursor.value.author, "Fred");
+  t.is(cursor.value.isbn, 123456);
+  cursor.continue();
+
+  await promiseFromRequest(request6);
+  cursor = request6.result;
+  t.is(cursor, null);
+
   db.close();
 
   t.pass();

packages/idb-bridge/src/MemoryBackend.ts

@@ -832,19 +832,32 @@ export class MemoryBackend implements Backend {
             break;
           }
         }
-        if (
+
-          unique &&
+        // Skip repeated index keys if unique results are requested.
-          indexKeys.length > 0 &&
+        let skip = false;
-          compareKeys(indexEntry.indexKey, indexKeys[indexKeys.length - 1]) ===
+        if (unique) {
-            0
+          if (
-        ) {
+            indexKeys.length > 0 &&
-          // We only return the first result if subsequent index keys are the same.
+            compareKeys(
-          continue;
+              indexEntry.indexKey,
+              indexKeys[indexKeys.length - 1],
+            ) === 0
+          ) {
+            skip = true;
+          }
+          if (
+            req.lastIndexPosition !== undefined &&
+            compareKeys(indexPos, req.lastIndexPosition) === 0
+          ) {
+            skip = true;
+          }
         }
-        indexKeys.push(indexEntry.indexKey);
+        if (!skip) {
-        primaryKeys.push(indexEntry.primaryKeys[primkeySubPos]);
+          indexKeys.push(indexEntry.indexKey);
-        numResults++;
+          primaryKeys.push(indexEntry.primaryKeys[primkeySubPos]);
-        primkeySubPos = forward ? 0 : indexEntry.primaryKeys.length - 1;
+          numResults++;
+        }
+        primkeySubPos += forward ? 1 : -1;
       }
 
       // Now we can collect the values based on the primary keys,