Add count() method support (#72)

core/src/jsMain/kotlin/Index.kt

@@ -18,4 +18,7 @@ public class Index internal constructor(
 
     override fun requestOpenKeyCursor(query: Key?, direction: Cursor.Direction): Request<IDBCursor?> =
         Request(index.openKeyCursor(query?.toJs(), direction.constant))
+
+    override fun requestCount(query: Key?): Request<Int> =
+        Request(index.count(query?.toJs()))
 }

core/src/jsMain/kotlin/ObjectStore.kt

@@ -18,4 +18,7 @@ public class ObjectStore internal constructor(
 
     override fun requestOpenKeyCursor(query: Key?, direction: Cursor.Direction): Request<IDBCursor?> =
         Request(objectStore.openKeyCursor(query?.toJs(), direction.constant))
+
+    override fun requestCount(query: Key?): Request<Int> =
+        Request(objectStore.count(query?.toJs()))
 }

core/src/jsMain/kotlin/Queryable.kt

@@ -8,4 +8,5 @@ public sealed class Queryable {
     internal abstract fun requestGetAll(query: Key?): Request<Array<dynamic>>
     internal abstract fun requestOpenCursor(query: Key?, direction: Cursor.Direction): Request<IDBCursorWithValue?>
     internal abstract fun requestOpenKeyCursor(query: Key?, direction: Cursor.Direction): Request<IDBCursor?>
+    internal abstract fun requestCount(query: Key?): Request<Int>
 }

core/src/jsMain/kotlin/Transaction.kt

@@ -97,6 +97,16 @@ public open class Transaction internal constructor(
         }
     }
 
+    public suspend fun Queryable.count(query: Key? = null): Int {
+        val request = requestCount(query).request
+        return request.onNextEvent("success", "error") { event ->
+            when (event.type) {
+                "error" -> throw ErrorEventException(event)
+                else -> request.result
+            }
+        }
+    }
+
     public fun ObjectStore.index(name: String): Index =
         Index(objectStore.index(name))
 }

core/src/jsTest/kotlin/Samples.kt

@@ -58,5 +58,15 @@ class Samples {
                 .first { it.age < 32 }
         }
         assertEquals("Charlie", charlie.name)
+
+        val count = database.transaction("customers") {
+            objectStore("customers").count()
+        }
+        assertEquals(4, count)
+
+        val countBelowThirtyTwo = database.transaction("customers") {
+            objectStore("customers").index("age").count(upperBound(32))
+        }
+        assertEquals(2, countBelowThirtyTwo)
     }
 }