SOURCE

var app = new Vue({
  el: '#app',
    data() {
      return {
        data5: [{
        label: '1',
        children: [{
          label: '2',
          children: [{
            label: '2-1'
          }, {
            label: '2-2'
          }]
        }, {
          label: '3',
          children: [{
            label: '3-1'
          }, {
            label: '3-2'
          }]
        }]
      }]
      }
    },
    mounted () {
        const data = JSON.parse(JSON.stringify(this.data5))
    const data1 = this.deep(data)
    console.log(data1)
    },
    methods: {
        deep (data) {
      data.forEach(element => {
        element.level = 1 // 这个怎么写成递归的深度
        if (element.children && element.children.length) {
          this.deep(element.children)
        }
      })
      return data
    }
        
    }
});

<div id="app">
  
</div>