element-plus/docs/examples/tree/custom-leaf.vue

<template>
  <el-tree
    style="max-width: 600px"
    :props="props"
    :load="loadNode"
    lazy
    show-checkbox
  />
</template>

<script lang="ts" setup>
import type { LoadFunction } from 'element-plus'

interface Tree {
  name: string
  leaf?: boolean
}

const props = {
  label: 'name',
  children: 'zones',
  isLeaf: 'leaf',
}

const loadNode: LoadFunction = (node, resolve) => {
  if (node.level === 0) {
    return resolve([{ name: 'region' }])
  }
  if (node.level > 1) return resolve([])

  setTimeout(() => {
    const data: Tree[] = [
      {
        name: 'leaf',
        leaf: true,
      },
      {
        name: 'zone',
      },
    ]

    resolve(data)
  }, 500)
}
</script>