JavaScript最新2023年面试题，高级面试题及附答案解析

//强制类型转换：
Boolean(0)   // =false - 零
Boolean(new object())   // =true - 对象
Number(undefined)       // =  NaN
Number(null)              // =0
String(null)              // ="null"
parseInt( )
parseFloat( )
JSON.parse( )
JSON.stringify ( )

（例如：x+"" //等价于String(x)  
\+x //等价于Number(x)  
x-0 //同上  
!!x //等价于Boolean(x),是双叹号）

基本步骤：
var xhr =null;//创建对象 
if(window.XMLHttpRequest){
       xhr = new XMLHttpRequest();
}else{
       xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
xhr.open(“方式”,”地址”,”标志位”);//初始化请求 
   xhr.setRequestHeader(“”,””);//设置http头信息 
xhr.onreadystatechange =function(){}//指定回调函数 
xhr.send();//发送请求

const carDetails = {
  name: "Ford Mustang",
  yearBought: 2005,
  getName(){
    return this.name;
  },
  isRegistered: true
};

console.log(carDetails.getName()); // Ford Mustang

var name = "Ford Ranger";
var getCarName = carDetails.getName;

console.log(getCarName()); // Ford Ranger

(function (){
 console.log(this);
})(); // 打印 "window" 对象

function iHateThis(){
  console.log(this);
}

iHateThis(); // 打印 "window" 对象

const myFavoriteObj = {
 guessThis(){
    function getName(){
      console.log(this.name);
    }
    getName();
 },
 name: 'Marko Polo',
 thisIsAnnoying(callback){
   callback();
 }
};

myFavoriteObj.guessThis(); // 打印 "window" 对象
myFavoriteObj.thisIsAnnoying(function (){
 console.log(this); // 打印 "window" 对象
});

const myFavoriteObj = {
 guessThis(){
  const self = this; // 把 this 值保存在 self 变量中
  function getName(){
    console.log(self.name);
  }
  getName();
 },
 name: 'Marko Polo',
 thisIsAnnoying(callback){
   callback();
  }
};

const myFavoriteObj = {
  guessThis(){
     const getName = () => { 
       console.log(this.name);
     }
     getName();
  },
  name: 'Marko Polo',
  thisIsAnnoying(callback){
   callback();
  }
};

//ES5 Version
 function Person(firstName, lastName, age, address){
    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;
    this.address = address;
 }

 Person.self = function(){
   return this;
 }

 Person.prototype.toString = function(){
   return "[object Person]";
 }

 Person.prototype.getFullName = function (){
   return this.firstName + " " + this.lastName;
 }  

 //ES6 Version
 class Person {
    constructor(firstName, lastName, age, address){
        this.lastName = lastName;
        this.firstName = firstName;
        this.age = age;
        this.address = address;
    }

    static self() {
       return this;
    }

    toString(){
       return "[object Person]";
    }

    getFullName(){
       return `${this.firstName} ${this.lastName}`;
    }
 }

//ES5 Version
Employee.prototype = Object.create(Person.prototype);

function Employee(firstName, lastName, age, address, jobTitle, yearStarted) {
  Person.call(this, firstName, lastName, age, address);
  this.jobTitle = jobTitle;
  this.yearStarted = yearStarted;
}

Employee.prototype.describe = function () {
  return `I am ${this.getFullName()} and I have a position of ${this.jobTitle} and I started at ${this.yearStarted}`;
}

Employee.prototype.toString = function () {
  return "[object Employee]";
}

//ES6 Version
class Employee extends Person { //Inherits from "Person" class
  constructor(firstName, lastName, age, address, jobTitle, yearStarted) {
    super(firstName, lastName, age, address);
    this.jobTitle = jobTitle;
    this.yearStarted = yearStarted;
  }

  describe() {
    return `I am ${this.getFullName()} and I have a position of ${this.jobTitle} and I started at ${this.yearStarted}`;
  }

  toString() { // Overriding the "toString" method of "Person"
    return "[object Employee]";
  }
}

class Something {

}

function AnotherSomething(){

}
const as = new AnotherSomething();
const s = new Something();

console.log(typeof Something); // "function"
console.log(typeof AnotherSomething); // "function"
console.log(as.toString()); // "[object Object]"
console.log(as.toString()); // "[object Object]"
console.log(as.toString === Object.prototype.toString); // true
console.log(s.toString === Object.prototype.toString); // true

console.log(Array.isArray(5));  // false
console.log(Array.isArray("")); // false
console.log(Array.isArray()); // false
console.log(Array.isArray(null)); // false
console.log(Array.isArray({ length: 5 })); // false

console.log(Array.isArray([])); // true