特别是return resolve([{ name: 'region1' }, { name: 'region2' }])这一句，搞不懂return返回了什么，resolve作为参数传入进来了，可resolve的定义在哪里，这个方法是如何使用的呢，请指教

<el-tree
:props="props"
:load="loadNode"
lazy
show-checkbox
@check-change="handleCheckChange">
</el-tree>

<script>
export default {

data() {
  return {
    props: {
      label: 'name',
      children: 'zones'
    },
    count: 1
  };
},
methods: {
  handleCheckChange(data, checked, indeterminate) {
    console.log(data, checked, indeterminate);
  },
  handleNodeClick(data) {
    console.log(data);
  },
  loadNode(node, resolve) {
    if (node.level === 0) {
      return resolve([{ name: 'region1' }, { name: 'region2' }]);
    }
    if (node.level > 3) return resolve([]);

    var hasChild;
    if (node.data.name === 'region1') {
      hasChild = true;
    } else if (node.data.name === 'region2') {
      hasChild = false;
    } else {
      hasChild = Math.random() > 0.5;
    }

    setTimeout(() => {
      var data;
      if (hasChild) {
        data = [{
          name: 'zone' + this.count++
        }, {
          name: 'zone' + this.count++
        }];
      } else {
        data = [];
      }

      resolve(data);
    }, 500);
  }
}

};
</script>