1 files changed, 58 insertions, 0 deletions
diff --git a/devtools/client/memory/dominator-tree-lazy-children.js b/devtools/client/memory/dominator-tree-lazy-children.js
new file mode 100644
index 000000000..85ae29a56
--- /dev/null
+++ b/devtools/client/memory/dominator-tree-lazy-children.js
@@ -0,0 +1,58 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * The `DominatorTreeLazyChildren` is a placeholder that represents a future
+ * subtree in an existing `DominatorTreeNode` tree that is currently being
+ * incrementally fetched from the `HeapAnalysesWorker`.
+ *
+ * @param {NodeId} parentNodeId
+ * @param {Number} siblingIndex
+ */
+function DominatorTreeLazyChildren(parentNodeId, siblingIndex) {
+  this._parentNodeId = parentNodeId;
+  this._siblingIndex = siblingIndex;
+}
+
+/**
+ * Generate a unique key for this `DominatorTreeLazyChildren` instance. This can
+ * be used as the key in a hash table or as the `key` property for a React
+ * component, for example.
+ *
+ * @returns {String}
+ */
+DominatorTreeLazyChildren.prototype.key = function () {
+  return `dominator-tree-lazy-children-${this._parentNodeId}-${this._siblingIndex}`;
+};
+
+/**
+ * Return true if this is a placeholder for the first child of its
+ * parent. Return false if it is a placeholder for loading more of its parent's
+ * children.
+ *
+ * @returns {Boolean}
+ */
+DominatorTreeLazyChildren.prototype.isFirstChild = function () {
+  return this._siblingIndex === 0;
+};
+
+/**
+ * Get this subtree's parent node's identifier.
+ *
+ * @returns {NodeId}
+ */
+DominatorTreeLazyChildren.prototype.parentNodeId = function () {
+  return this._parentNodeId;
+};
+
+/**
+ * Get this subtree's index in its parent's children array.
+ *
+ * @returns {Number}
+ */
+DominatorTreeLazyChildren.prototype.siblingIndex = function () {
+  return this._siblingIndex;
+};
+
+module.exports = DominatorTreeLazyChildren;