Add Node.contains() method that returns a boolean value indicating wh…

…ether a node is a descendant of a given node or not (closes #2).

src/node.js

@@ -11,6 +11,18 @@ class Node {
 
         this.children = this.children || [];
     }
+    // Returns a boolean value indicating whether a node is a descendant of a given node or not.
+    // @param {object} node Specifies the node that may be contained by (a descendant of) a specified node.
+    // @return {boolean} Returns true if a node is a descendant of a specified node, otherwise false. A descendant can be a child, grandchild, great-grandchild, and so on.
+    contains(node) {
+        while ((node instanceof Node) && (node !== this)) {
+            if (node.parent === this) {
+                return true;
+            }
+            node = node.parent;
+        }
+        return false;
+    }
     // Gets a child node at the specified index.
     // @param {number} The index of the child node.
     // @return {object} Returns an object that defines the node, null otherwise.

test/index.js

@@ -565,12 +565,28 @@ test('[flatten] Ensure the parent node is an instance of Node after calling flat
     t.end();
 });
 
-test('[node] getChildren/getParent/getFirstChild/getPreviousSibling/getNextSibling', (t) => {
+test('[node] Node API', (t) => {
     const tree = JSON.parse(fixtures.tree);
     const nodes = flatten(tree, { openAllNodes: true });
     const root = _.find(nodes, node => node.id === '<root>');
     const alpha = _.find(nodes, node => node.id === 'alpha');
     const bravo = _.find(nodes, node => node.id === 'bravo');
+    const juliet = _.find(nodes, node => node.id === 'juliet');
+
+    // contains
+    t.equal(root.contains(null), false);
+    t.equal(root.contains(undefined), false);
+    t.equal(root.contains({}), false);
+    t.equal(root.contains([]), false);
+    t.equal(root.contains(root), false);
+    t.equal(root.contains(alpha), true);
+    t.equal(root.contains(bravo), true);
+    t.equal(root.contains(juliet), true);
+    t.equal(alpha.contains(bravo), false);
+    t.equal(alpha.contains(juliet), false);
+    t.equal(bravo.contains(alpha), false);
+    t.equal(bravo.contains(juliet), true);
+    t.equal(juliet.contains(root), false);
 
     // hasChildren
     t.same(root.hasChildren(), true);