feat: implement backend for import/export

Related to #2

Signed-off-by: Matej Focko <mfocko@redhat.com>

node.js

@@ -130,6 +130,40 @@ function nodeMaximum(node) {
     return node;
 }
 
+function nodeExport(node) {
+    if (!node) {
+        return null;
+    }
+
+    return {
+        value: node.value,
+        rank: node.rank,
+        left: nodeExport(node.left),
+        right: nodeExport(node.right),
+    };
+}
+
+function nodeImport(json) {
+    if (!json) {
+        return null;
+    }
+
+    let node = new Node(json.value);
+    node.rank = json.rank;
+
+    if (json.left) {
+        node.left = nodeImport(json.left);
+        node.left.parent = node;
+    }
+
+    if (json.right) {
+        node.right = nodeImport(json.right);
+        node.right.parent = node;
+    }
+
+    return node;
+}
+
 class Node {
     constructor(value, left, right, parent) {
         this.value = value;