flow like the river

BACK_BACK/node_modules/d3-selection/src/selection/order.js

@@ -0,0 +1,13 @@
+export default function() {
+
+  for (var groups = this._groups, j = -1, m = groups.length; ++j < m;) {
+    for (var group = groups[j], i = group.length - 1, next = group[i], node; --i >= 0;) {
+      if (node = group[i]) {
+        if (next && node.compareDocumentPosition(next) ^ 4) next.parentNode.insertBefore(node, next);
+        next = node;
+      }
+    }
+  }
+
+  return this;
+}