async...await串行并行

function fun1() {
      return new Promise(resolve => {
        setTimeout(() => {
          resolve(1)
        }, 2000)
      })
    }
    function fun2() {
      return new Promise(resolve => {
        setTimeout(() => {
          resolve(2)
        }, 3000)
      })
    }
    // 并行
    async function fun6() {
      console.time('fun6')
      let res = await Promise.all([fun1(),fun2()])
      console.log(res) // [1, 2]
      console.timeEnd('fun6')
    }
    fun6() // 3s

    // 并行
    async function fun8() {
      console.time('fun8')
      let a = fun1()
      let b = fun2()
      let c = await a
      let d = await b
      console.log(c) // 1
      console.log(d) // 2
      console.timeEnd('fun8')
    }
    fun8() // 3s

    // 串行
    async function fun7() {
      console.time('fun7')
      await fun1()
      await fun2()
      console.timeEnd('fun7')
    }
    fun7() // 5s