text: let show1 = function () {
      console.log('abc')
  }
  
  let show2 = () => {
      console.log('abc')
  }
  
  show1() // 调用函数
  show2()
  
  let show4 = function (a) {
      return a*2
  }
  
  let show5 = a => a * 2  //简洁，类似python lambda 函数
  
  console.log(show4(10))
  console.log(show5(10))
  