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demo/documentation/components/tree/enUS/async.demo.md

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+# Async Loading
+
+After set `remote`, use `on-load` callback to load data. When loading async, all nodes with `isLeaf` set to `false` and `chilren`'s type is not `Array` will be reckon as unloaded nodes.
+
+```html
+<n-tree
+  block-node
+  checkable
+  remote
+  :data="data"
+  :checked-keys="checkedKeys"
+  :on-load="handleLoad"
+  @update:checked-keys="handleCheckedKeysChange"
+  :expanded-keys="expandedKeys"
+  @update:expanded-keys="handleExpandedKeysChange"
+/>
+```
+
+```js
+function createData () {
+  return [
+    {
+      label: nextLabel(),
+      key: 1,
+      isLeaf: false
+    },
+    {
+      label: nextLabel(),
+      key: 2,
+      isLeaf: false
+    }
+  ]
+}
+
+function nextLabel (currentLabel) {
+  if (!currentLabel) return 'Out of Tao, One is born'
+  if (currentLabel === 'Out of Tao, One is born') return 'Out of One, Two'
+  if (currentLabel === 'Out of One, Two') return 'Out of Two, Three'
+  if (currentLabel === 'Out of Two, Three') {
+    return 'Out of Three, the created universe'
+  }
+  if (currentLabel === 'Out of Three, the created universe') {
+    return 'Out of Tao, One is born'
+  }
+}
+
+export default {
+  data () {
+    return {
+      data: createData(),
+      expandedKeys: [],
+      checkedKeys: []
+    }
+  },
+  methods: {
+    handleExpandedKeysChange (expandedKeys) {
+      this.expandedKeys = expandedKeys
+    },
+    handleCheckedKeysChange (checkedKeys) {
+      this.checkedKeys = checkedKeys
+    },
+    handleLoad (node) {
+      return new Promise((resolve, reject) => {
+        setTimeout(() => {
+          node.children = [
+            {
+              label: nextLabel(node.label),
+              key: node.key + nextLabel(node.label),
+              isLeaf: false
+            }
+          ]
+          this.data = Array.from(this.data)
+          resolve()
+        }, 1000)
+      })
+    }
+  }
+}
+```