如下代码输出多少？如果想输出3，那如何改造代码？

var fnArr = [];
for (var i = 0; i < 10; i ++) {
  fnArr[i] =  function(){
    return i
  };
}
console.log( fnArr[3]() )

    var fnArr = []
    for (var i = 0; i < 10; i ++){
    fnArr[i] = (function(j){
    return function(){
    return j
    }
    })(i)
    }
    console.log( fnArr[3](https://xiedaimala.com/remarks/831884cc-0f98-4dfc-943b-a5ae64cc0a7f "null") )

    var fnArr = []
    for (var i = 0; i < 10; i ++){
    (function(i){
    fnArr[i] = function(){
    return i
    }
    })(i)
    }
    console.log( fnArr[3](https://xiedaimala.com/remarks/831884cc-0f98-4dfc-943b-a5ae64cc0a7f "null") )

    var fnArr = []
    for (let i = 0; i < 10; i ++){
    fnArr[i] = function(){
    return i
    }
    }
    console.log( fnArr[3](https://xiedaimala.com/remarks/831884cc-0f98-4dfc-943b-a5ae64cc0a7f "null") )

封装一个 Car 对象。

var Car = (function(){
   var speed = 0;
   //补充
   return {
      setSpeed: setSpeed,
      get: get,
      speedUp: speedUp,
      speedDown: speedDown
   }
})()
Car.set(30)
Car.get() //30
Car.speedUp()
Car.get() //31
Car.speedDown()
Car.get()  //30

  var Car = (function(){
  var speed = 0;
  function set(s){
  speet = s
  }
  function get(){
  return speed
  }
  function speedUp(){
  speed++
  }
  function speedDown(){
  speed--
  }
  return {
  setSpeed: setSpeed,
  get: get,
  speedUp: speedUp,
  spedDown: speedDown,
  }
  })()
  Car.set(30)
  Car.get()
  Car.speedUp()
  Car.get()
  Car.speedDown()
  Car.get()

如下代码输出多少？如何连续输出 0,1,2,3,4？

for(var i=0; i<5; i++){
  setTimeout(function(){
    console.log('delayer:' + i )
  }, 0)
}

    for(var i=0; i<5; i++){
    (function(j){
    setTimeout(function(){
    console.log('delayer:' + j)
    },0)
    })(i)
    }

    for(var i=0; i<5; i++){
    setTimeout((function(j){
    return function(){
    console.log('delayer:' + j)
    }
    }(i)),0)
    }

如下代码输出多少？

function makeCounter() {
  var count = 0

  return function() {
    return count++
  };
}

var counter = makeCounter()
var counter2 = makeCounter();

console.log( counter() ) // 0
console.log( counter() ) // 1

console.log( counter2() ) // ?
console.log( counter2() ) // ?

  0
  1
为什么呢?

补全代码，实现数组按姓名、年纪、任意字段排序。

var users = [
  { name: "John", age: 20, company: "Baidu" },
  { name: "Pete", age: 18, company: "Alibaba" },
  { name: "Ann", age: 19, company: "Tecent" }
]

users.sort(byField('age'))
users.sort(byField('company'))

    var users = [
    {name: "John", age: 20, company: "Baidu"},
    {name: "Pete", ag: 18, company: "Alibaba"},
    {name: "Ann", age: 19, company: "Tecent"}
    ]
    users.sort(byName)
    users.sort(byAge)
    users.sort(byField('surnamme'))
    //
    function byName(user1,user2){
    return user1.name>user2.name
    }
    function byAge(user1,user2){
    return user1.age>user2.age
    }
    function byField(field){
    return function(user1,user2){
    return user1[field] > user2[field]
    }
    }
    users.sort(byField('surname'))

写一个 sum 函数，实现如下调用方式。

console.log( sum(1)(2) ) // 3
console.log( sum(5)(-1) ) // 4

    console.log(sum(1)(2))
    console.log(sum(5)(-1))
    //
    function sum(b){
    return function(a){
    return a + b
    }
    }