一、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]() ) 

10

//方法一
var fnArr = []
for(var i = 0; i < 10; i++){
    fnArr[i] = (function(j){
      return function(){
        return j
      }
    })(i)
}
console.log( fnArr[3]() )
//方法二
var fnArr = []
for(var i = 0; i < 10; i++){
  (function(i){
    fnArr[i] = function(){
      return i
    }
  })(i)   
}
console.log( fnArr[3]() )
//方法三
var fnArr = [];
for (let i = 0; i < 10; i ++) {
  fnArr[i] =  function(){
    return i
  };
}
console.log( fnArr[3]() )

二、封装一个 Car 对象。

var Car = (function(){
   var speed = 0;
   function setSpeed(s){
     speed = s
   }
   function get(){
     return speed
   }
  function speedUp(){
    return speed++
  }
  function speedDown(){
    return speed--
  }
   return {
      setSpeed: setSpeed,
      get: get,
      speedUp: speedUp,
      speedDown: speedDown
   }
})()
Car.setSpeed(30)
console.log(Car.get()) //30
Car.speedUp()
console.log(Car.get()) //31
Car.speedDown()
console.log(Car.get())  //30

三、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)
}

//方法一
for(var i=0; i<5; i++){
  (function(j){
    setTimeout(function(){
    console.log('delayer:' + j )
    }, 0)
  })(i)
}
//方法二
for(var i=0; i<5; i++){
  setTimeout((function(j){
    return function(){
    console.log('delayer:' + j )
    }
  })(i),0)
}

四、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
0
1

有两个不同的作用域，对象是不一样的

五、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", age: 18, company: "Alibaba" },
  { name: "Ann", age: 19, company: "Tecent" }
]
function byField(field){
  return function(a, b){
    return a[field] > b[field]
  }
}
users.sort(byField('company'))
users.sort(byField('age'))

六、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

function sum(a){
    return fuction(b){
        return a + b
    }
}