Use modules.

imports/Spectral/Component/SideNavButton.qml

@@ -0,0 +1,25 @@
+import QtQuick 2.9
+import QtQuick.Controls 2.2
+import QtQuick.Layouts 1.3
+import QtQuick.Controls.Material 2.2
+
+import "qrc:/js/util.js" as Util
+
+ItemDelegate {
+    property var page
+    property bool selected: stackView.currentItem === page
+    property color highlightColor: Material.accent
+
+    Rectangle {
+        width: selected ? 4 : 0
+        height: parent.height
+
+        color: highlightColor
+
+        Behavior on width {
+            PropertyAnimation { easing.type: Easing.InOutCubic; duration: 200 }
+        }
+    }
+
+    onClicked: Util.pushToStack(stackView, page)
+}