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]() ) 

封装一个 Car 对象。

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

var Car = (function(){
   var speed = 0;
   function setSpeed(s){
       speed = s
   }
   function get(){
      return speed
   }
   function speedUp(){
      speed++
   }
   function speedDown(){
      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

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)
}

输出 5 5 5 5 5
连续输出 0,1,2,3,4

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

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() ) // 0
console.log( counter2() ) // 1

因为counter和counter2有不同的作用域

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'))

先跳过碰到点问题

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 function(b) {
    return a + b
  }
}

函数柯里化-只传递给函数一部分参数来调用它，让它返回一个函数去处理剩下的参数。