jacline: Add ViewBase

dumbo-jacline/src/main/java/com/kohlschutter/dumbo/js/ViewBase.java

@@ -0,0 +1,29 @@
+package com.kohlschutter.dumbo.js;
+
+import java.util.Objects;
+
+import elemental2.dom.Element;
+import elemental2.dom.Node;
+
+public abstract class ViewBase {
+  private final Node parent;
+
+  protected ViewBase(Node parentNode) {
+    this.parent = Objects.requireNonNull(parentNode, "parentNode");
+  }
+
+  protected Element querySelector(String selectors) {
+    return parent.querySelector(selectors);
+  }
+
+  protected Node getParentNode() {
+    return parent;
+  }
+
+  protected Element querySelector(Element ref, String selectors) {
+    if (ref == null) {
+      return null;
+    }
+    return ref.querySelector(selectors);
+  }
+}