1.1 在原型上重写unshift

var arr = ['d', 'e', 'f'];
Array.prototype.myUnshift = function(){
  var pos = 0,
      len = arguments.length;
  for(var i = 0; i < len; i++){
    this.splice(pos, 0, arguments[i]);
    pos ++;
  }
  return this.length;
}
arr.myUnshift('a', 'b', 'c');
console.log(arr);//['a', 'b', 'c', 'd', 'e', 'f']

思路，利用splice，第一个参数是下标位置，每次循环加1，因为是添加，第二个参数填0就是不截取，每次循环把第三个值重新添加进去.

重点，arguments是function的实参列表，其实是类数组，可以利用Array.prototype.slice.call(arguments)变成数组，如

function test(){
  console.log(arguments);//[1, 2, 3, 4, callee: ƒ, Symbol(Symbol.iterator): ƒ]
  console.log(Array.prototype.slice.call(arguments));//[1, 2, 3, 4]
}
test(1, 2, 3, 4);

第二种方法，利用concat

var arr2 = ['d', 'e', 'f'];
Array.prototype.myUnshift2 = function(){
  var argArr = Array.prototype.slice.call(arguments);
  return  argArr.concat(this);
}
var newArray = arr2.myUnshift2('a', 'b', 'c');
console.log(newArray);

1.2数组按照元素的字节数排序

function getBytes(str){
  var bytes = str.length;//先让所有的元素算一个字节
  for(var i = 0; i < str.length; i++){
    if(str.charCodeAt(i) > 255){//注意，unicode 0-255是算1个字节，256-之后算2个字节
      bytes++;
    }
  }
  return bytes;
}
console.log(getBytes('我爱你'));//6
var arr3 = ['我爱你', 'OK', 'Hello', '你说WHAT', '可以'];
arr3.sort(function(a, b){
  return getBytes(a) - getBytes(b);
})
console.log(arr3);//['OK', '可以', 'Hello', '我爱你', '你说WHAT']

2.1封装typeof

思路，typeof能返回的值 number boolean object function undefined，null返回的是object

function myTypeof(val){
  var type = typeof(val),
      toStr = Object.prototype.toString,
      res = {
        '[object Array]': 'array',
        '[object Object]': 'object',
        '[object Number]': 'object number',
        '[object String]': 'object string',
        '[object Boolean]': 'object boolean'
      };
  if(val === null){
    return 'null';
  }else if(type === 'object'){
    var ret = toStr.call(val);
    return res[ret];
  }else{
    return type;
  }
}
console.log(myTypeof());

2.2数组去重

思路，利用对象键名的不重复性

var arr4 = [0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 'a', 'a'];
Array.prototype.unique = function(){
  var temp = {},
      newArr = [];
  for(var i = 0;i < this.length; i++){
    if(!temp.hasOwnProperty(this[i])){//注意，如果写成!temp[this[i]]，！0就是true，所以0过滤不掉
      temp[this[i]] = this[i];
      newArr.push(this[i]); 
    }
  }
  return newArr;
}
console.log(arr4.unique());

2.3字符串去重

同理

var str = '0000111122222546545644445556aaabbc';
String.prototype.unique2 = function(){
  var temp = {},
      newStr = '';
  for(var i = 0;i < this.length; i++){
    if(!temp.hasOwnProperty(this[i])){
      temp[this[i]] = this[i];
      newStr += this[i]; 
    }
  }
  return newStr;
}
console.log(str.unique2());

2.4面试题，找出第一个不重复的值

思路，还是同样的，让对象的valua值计数，出现几次加几次，最后遍历，返回打印第一个键名

var str2 = 'wiiiieeeewrrtppaettttbfjgldyyuuuuuuk';
function unique3(str){
  var temp = {};
  for(var i = 0; i < str.length; i++){
    if(temp.hasOwnProperty(str[i])){
      temp[str[i]]++;
    }else{
      temp[str[i]] = 1;
    }
  }
  for(var key in temp){
    if(temp[key] === 1){
      return key;
    }
  }
}
console.log(unique3(str2));//a

3.1面试题一，闭包

function Test(a, b, c){
  var d = 0;
  this.a = a;
  this.b = b;
  this.c = c;
  function e(){
    d++;
    console.log(d);
  }
  this.f = e;
}
var test1 = new Test();
test1.f();//1
test1.f();//2
var test2 = new Test();
test2.f();//1

3.2面试题二

function test3(){
  console.log(typeof(arguments));//object
}
test3();

3.3面试题三

var test4 = function a(){
  return 'a';
}
console.log(typeof(a));//undefined,函数表达式是忽略函数名的,typeof里放一个未被声明的变量就是undefined
var test5 = function a(){
  console.log(test5.name);//a
}
test5();

面试题四，如何优化这个函数

function test6(day){
  switch(day){
    case 1:
      console.log('Mon');
      break;
    case 2:
      console.log('Tue');
      break;
    case 3:
      console.log('Wed');
      break;
    case 4:
      console.log('Thu');
      break;
    case 5:
      console.log('Fri');
      break;
    case 6:
      console.log('Sat');
      break;
    case 7:
      console.log('Sun');
      break;
    default:
      console.log('I don\'t know');
  }
}
test6(4);//Thu

优化

function test7(day){
  var weekday = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
  return weekday[day - 1] !== undefined ? console.log(weekday[day - 1]) : console.log('I don\'t know');
}
test7(0);