add EventTarget implementation (#2377)

js/dom_util.ts

@@ -0,0 +1,83 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+// Utility functions for DOM nodes
+import * as domTypes from "./dom_types";
+
+export function isNode(nodeImpl: domTypes.EventTarget | null): boolean {
+  return Boolean(nodeImpl && "nodeType" in nodeImpl);
+}
+
+export function isShadowRoot(nodeImpl: domTypes.EventTarget | null): boolean {
+  return Boolean(
+    nodeImpl &&
+      nodeImpl.nodeType === domTypes.NodeType.DOCUMENT_FRAGMENT_NODE &&
+      "host" in nodeImpl
+  );
+}
+
+export function isSlotable(nodeImpl: domTypes.EventTarget | null): boolean {
+  return Boolean(
+    nodeImpl &&
+      (nodeImpl.nodeType === domTypes.NodeType.ELEMENT_NODE ||
+        nodeImpl.nodeType === domTypes.NodeType.TEXT_NODE)
+  );
+}
+
+// https://dom.spec.whatwg.org/#node-trees
+// const domSymbolTree = Symbol("DOM Symbol Tree");
+
+// https://dom.spec.whatwg.org/#concept-shadow-including-inclusive-ancestor
+export function isShadowInclusiveAncestor(
+  ancestor: domTypes.EventTarget | null,
+  node: domTypes.EventTarget | null
+): boolean {
+  while (isNode(node)) {
+    if (node === ancestor) {
+      return true;
+    }
+
+    if (isShadowRoot(node)) {
+      node = node && node.host;
+    } else {
+      node = null; // domSymbolTree.parent(node);
+    }
+  }
+
+  return false;
+}
+
+export function getRoot(
+  node: domTypes.EventTarget | null
+): domTypes.EventTarget | null {
+  let root = node;
+
+  // for (const ancestor of domSymbolTree.ancestorsIterator(node)) {
+  //   root = ancestor;
+  // }
+
+  return root;
+}
+
+// https://dom.spec.whatwg.org/#retarget
+export function retarget(
+  a: domTypes.EventTarget | null,
+  b: domTypes.EventTarget
+): domTypes.EventTarget | null {
+  while (true) {
+    if (!isNode(a)) {
+      return a;
+    }
+
+    const aRoot = getRoot(a);
+
+    if (aRoot) {
+      if (
+        !isShadowRoot(aRoot) ||
+        (isNode(b) && isShadowInclusiveAncestor(aRoot, b))
+      ) {
+        return a;
+      }
+
+      a = aRoot.host;
+    }
+  }
+}