利用promise 让 函数按序执行

<template>
  <div>
    <el-button @click="btn">按钮</el-button>
  </div>

</template>

<script>
export default {
  data() {
    return {}
  },
  mounted() {

  },
  methods:{
    btn() {
      this.a().then(this.b).then(this.c)
    },
    // async btn(){
    //    await this.a()
    //    await this.b()
    //    await this.c()
    // },
      a(){
      return new Promise(((resolve,reject) => {
        setTimeout(()=>{
          console.log(1)
          resolve()
        },3000)
      }))
    },
      b(){
      return new Promise(resolve => {
        setTimeout(()=>{
          console.log(2)
          resolve()
        },2000)
      })
    },
      c(){
      return new Promise(resolve =>{
        setTimeout(()=>{
          console.log(3)
          resolve()
        },1000)
      })
    },

  }
}
</script>