var single = a => a
single('hello, world') // 'hello, world'

var log = () => {
 alert('no param')
}

var add = (a, b) => a + b
add(3, 8) // 11

var add = (a, b) => {
 if (typeof a == 'number' && typeof b == 'number') {
  return a + b
 } else {
  return 0
 }
}

var getHash = arr => {
 // ...
 return ({
  name: 'Jack',
  age: 33
 })
}

document.addEventListener('click', ev => {
 console.log(ev)
})

var arr = [1, 9 , 2, 4, 3, 8].sort((a, b) => {
 if (a - b > 0 ) {
  return 1
 } else {
  return -1
 }
})
arr // [1, 2, 3, 4, 8, 9]

var func = a => a
console.log(typeof func); // "function"

console.log(func instanceof Function); // true

obj = {
 data: ['John Backus', 'John Hopcroft'],
 init: function() {
  document.onclick = ev => {
   alert(this.data) // ['John Backus', 'John Hopcroft']
  }
  // 非箭頭函數(shù)
  // document.onclick = function(ev) {
  //  alert(this.data) // undefined
  // }
 }
}
obj.init()

var Person = (name, age) => {
 this.name = name
 this.age = age
}
var p = new Func('John', 33) // error

var func = () => {
 console.log(arguments)
}
func(55) //