Restructure code

mixins/tree-load-children.js

@@ -0,0 +1,62 @@
+export const TreeLoadChildrenMixin = (superClass) => class TreeLoadChildrenMixin extends superClass {
+  async _loadChildrenForExpanded(key, source, originalEvent, nodeHint = null, pathHint = null) {
+    if (typeof this.loadChildren !== 'function') return;
+
+    const node = nodeHint ?? this._findNodeByKey(key);
+    if (!node) return;
+
+    const controller = new AbortController();
+    const seq = ++this._childLoadSeq;
+    const previous = this._childLoadControllers.get(key);
+    if (previous) {
+      try { previous.abort(); } catch (e) { }
+    }
+    this._childLoadControllers.set(key, controller);
+
+    this._updateNodeStatesByKey(key, (n) => {
+      const states = Array.isArray(n.states) ? n.states : [];
+      const next = states.filter((s) => s !== 'loaded');
+      if (!next.includes('loading')) next.push('loading');
+      return { ...n, states: next };
+    });
+
+    try {
+      const ctx = {
+        node,
+        key,
+        path: Array.isArray(pathHint) ? pathHint : key.split('/').filter(Boolean),
+        signal: controller.signal,
+        source,
+        originalEvent,
+      };
+
+      await Promise.resolve(this.loadChildren(ctx));
+      if (controller.signal.aborted) return;
+      if (this._childLoadControllers.get(key) !== controller) return;
+      if (seq !== this._childLoadSeq) return;
+
+      this._updateNodeStatesByKey(key, (n) => {
+        const states = Array.isArray(n.states) ? n.states : [];
+        const next = states.filter((s) => s !== 'loading');
+        if (!next.includes('loaded')) next.push('loaded');
+        return { ...n, states: next };
+      });
+    } catch (err) {
+      if (controller.signal.aborted) return;
+      this._updateNodeStatesByKey(key, (n) => {
+        const states = Array.isArray(n.states) ? n.states : [];
+        const next = states.filter((s) => s !== 'loading');
+        return { ...n, states: next };
+      });
+      this.dispatchEvent(new CustomEvent('node-children-error', {
+        detail: { key, node, error: err, source, originalEvent },
+        bubbles: true,
+        composed: true,
+      }));
+    } finally {
+      if (this._childLoadControllers.get(key) === controller) {
+        this._childLoadControllers.delete(key);
+      }
+    }
+  }
+};