walkUp function

src/index-fn.js

@@ -11,3 +11,4 @@ export {default as map}           from "./map.js";
 export {default as walk}          from "./walk.js";
 export {default as transform}     from "./transform.js";
 export {default as reduce}        from "./reduce.js";
+export {default as walkUp}        from "./walkUp.js";

src/walkUp.js

@@ -0,0 +1,19 @@
+import { getParent } from "./parents.js";
+import { assertParentPointers } from "./util.js";
+
+/**
+ * Walk up the tree from the given node, calling the callback on each node.
+ * @param {object} node
+ * @param {function} callback
+ * @returns {any} The first non-undefined value returned by the callback, otherwise undefined
+ */
+export default function walkUp (node, callback) {
+	while (node) {
+		const ret = callback(node);
+		if (ret !== undefined) {
+			return ret;
+		}
+		assertParentPointers.call(this, node, "Cannot walk up the tree from a node with no parent pointer.");
+		node = getParent.call(this, node);
+	}
+}

test/walkUp.js

@@ -0,0 +1,26 @@
+import walkUp from "../src/walkUp.js";
+import trees from "./utils/trees.js";
+import updateParents from "../src/updateParents.js";
+import copy from "./utils/copy.js";
+
+const tree = copy(trees[0]);
+updateParents(tree);
+
+export default {
+	name: "walkUp()",
+	run (node, cb) {
+		return walkUp(node, cb);
+	},
+	tests: [
+		{
+			name: "No callback",
+			args: [tree.right, () => {}],
+			expect: undefined
+		},
+		{
+			name: "Callback returns a value",
+			args: [tree.right, n => n.name === "1" ? n : undefined],
+			expect: tree
+		}
+	]
+};