let answer;function fn(){//如果此時沒有將變量變量提升到這里，answer應該取外層answer的值console.log(answer); //Uncaught ReferenceError: Cannot access "answer" before initializationlet answer=42;}

//變量提升先于函數(shù)提升,提升后被函數(shù)聲明function覆蓋,所以就算換了順序也是functionfunction a(){}var a ;console.log(typeof a); //functionvar f1 = function () {    console.log(1);}function f1 () {    console.log(2);}f1() ; //1//變量提升后var f1;//變量提升function f1(){};//函數(shù)提升f1 = function () {    console.log(1);}f1() ;

var a = 10;  function aaa() {    alert(a);}function bbb() {    var a = 20;    aaa();}bbb();

var foo = 1;function bar () {    console.log(foo);    var foo = 10;    console.log(foo);}bar();//變量提升后var foo = 1;function bar () {var foo = undefined;    console.log(foo); //undefined    foo = 10;    console.log(foo);//10}bar();

(function(){  var a = 1;  console.log("內(nèi)部a:", a);})();

var __const = function __const(data, value) {this.data = value // 把要定義的data掛載到某個對象，并賦值valueObject.defineProperty(this，data, { // 利用Object.defineProperty的能力劫持當前對象，并修改其屬性描述符enumerable: false,configurable: false,get: function () {return value},set: function (data) {if (data !== value) { // 當要對當前屬性進行賦值時，則拋出錯誤！throw new TypeError("Assignment to constant variable.")} else {return value}}})}//然后和立即執(zhí)行函數(shù)結(jié)合(function(){ var obj = {}_const.call(obj,"a",10)})()//當執(zhí)行完畢后，全局上就不會有obj，也不會有obj.a這個變量，進而實現(xiàn)了塊級作用域的功能

function a(){  a.name ="aaa";  return this.name;}var b = {  a,  name:"bbb",  getName:function(){    return this.name;  }}var c =b.getName;console.log(a()); //this指向window,window上沒有name,所以輸出undefinedconsole.log(b.a()); //b.a 是function,b調(diào)用a函數(shù)，所以this指向b，所以輸出"bbb"console.log(b.getName);//通過b調(diào)用getName，所以getName指向b,所以輸出"bbb"console.log(c());//c是function，this指向window，window上沒有name,所以輸出undefined

//從第二個參數(shù)開始依次傳入，所以接收時使用rest參數(shù)Function.prototype.call=function(obj,...args){obj = obj || window;args = args ? args : [];//給obj新增一個獨一無二的屬性以免覆蓋原有屬性    const key = Symbol()obj[key] = this;const res = obj[key](...args);delete obj[key];return res;}

Function.prototype.apply=function(obj,args){obj = obj || window;args = args ? args : [];//給obj新增一個獨一無二的屬性以免覆蓋原有屬性    const key = Symbol()obj[key] = this;const res = obj[key](...args);delete obj[key];return res;}

Function.prototype.bind=function(obj,...args){obj = obj || window;args = args ? args : [];return (...args2) => {return this.apply(obj,[...args,...args2])}}

function foo(){var a=2;function bar(){ //覆蓋foo()內(nèi)部作用域的閉包console.log(a++);}return bar;}var bar = foo(); //foo執(zhí)行創(chuàng)建一個執(zhí)行上下文環(huán)境，由于bar引用了其內(nèi)部變量，也就是bar持有foo本次執(zhí)行上下文的引用，foo本次的執(zhí)行上下文不會被銷魂bar();//2bar();//3var fn = foo(); //foo執(zhí)行創(chuàng)建一個新的執(zhí)行上下文環(huán)境，fn持有了foo本次執(zhí)行上下文的引用fn();//2

//使用形式，綁定時候throttle函數(shù)就會執(zhí)行,所以this是windowwindow.addEventListener("scroll",throttle(()=>{},500))/*思路需要記錄上一次觸發(fā)的時間，才可以和當前時間比較，是否超過了間隔時間第一次必然立刻觸發(fā)*/function throttle(callback,wait){let pre = new Date();//這里的this是windowreturn function(...args){//這里的this是綁定的DOMconst now = new Date();if(now-pre>=wait){callback.apply(this,args);pre = now;}}}/*使用setTimeout實現(xiàn)第一次需要延遲delay后觸發(fā)*/function throttle(callback,delay){let timer = null;//這里的this是windowreturn function(...args){if(timer){//說明已經(jīng)觸發(fā)了return;}timer = setTimeout(()=>{callback.apply(this,args);timer = null;},delay)}}

function debounce(callback,delay){let timer = null;//這里的this是windowreturn function(){if(timer){//說明已經(jīng)觸發(fā)了clearTimeout(timer);}timer = setTimeout(()=>{callback.apply(this,arguments);timer = null;},delay)}}//立即執(zhí)行function debounce(func,delay) {  let timeout;  return function (...args) {      if (timeout) clearTimeout(timeout);      const callNow = !timeout;      timeout = setTimeout(() => {          timeout = null;      }, delay)      if (callNow) func.apply(this, args)  }}

//subject 被觀察者class Subject {  constructor() {    this.observerList = [];  }  addObserver(observer) {    this.observerList.push(observer);  }  removeObserver(observer) {    const index = this.observerList.findIndex(o => o.name === observer.name);    this.observerList.splice(index, 1);  }  notifyObservers(message) {    const observers = this.observeList;    observers.forEach(observer => observer.notified(message));  }}//Observer 觀察者class Observer {  constructor(name, subject) {    this.name = name;    if (subject) {      subject.addObserver(this);    }  }  notified(message) {    console.log(this.name, "got message", message);  }}//使用const subject = new Subject();const observerA = new Observer("observerA", subject);const observerB = new Observer("observerB");subject.addObserver(observerB);subject.notifyObservers("Hello from subject");subject.removeObserver(observerA);subject.notifyObservers("Hello again");

//事件調(diào)度中心class PubSub {  constructor() {        // 存儲格式: warTask: [], routeTask: []        // {訂閱事件:[回調(diào)1,回調(diào)2...],訂閱事件2:[回調(diào)1,回調(diào)2..]}        this.events = {}     }     // 訂閱方法 訂閱哪個類型type就把對應的回調(diào)函數(shù)放入      subscribe(type, cb) {         if (!this.events[type]) {            this.events[type] = [];        }        this.events[type].push(cb);     }     // 發(fā)布方法    publish(type, ...args) {        if (this.events[type]) {            this.events[type].forEach(cb => cb(...args))        }    }// 取消訂閱方法 的某一個類型的某一個回調(diào)    unsubscribe(type, cb) {        if (this.events[type]) {            const cbIndex = this.events[type].findIndex(e=> e === cb)            if (cbIndex != -1) {                this.events[type].splice(cbIndex, 1);            }        }        if (this.events[type].length === 0) {            delete this.events[type];        }    }}//測試let pubsub = new PubSub();//訂閱pubsub.subscribe("warTask", function (taskInfo){    console.log("宗門殿發(fā)布戰(zhàn)斗任務，任務信息:" + taskInfo);})pubsub.subscribe("routeTask", function (taskInfo) {    console.log("宗門殿發(fā)布日常任務，任務信息:" + taskInfo);});pubsub.subscribe("allTask", function (taskInfo) {    console.log("宗門殿發(fā)布五星任務，任務信息:" + taskInfo);});//發(fā)布pubsub.publish("warTask", "獵殺時刻");pubsub.publish("allTask", "獵殺時刻");pubsub.publish("routeTask", "種樹澆水");pubsub.publish("allTask", "種樹澆水");

//循環(huán)引用:b中引用了c，c中又有bobj = {b:["a","f"],c:{h:20}}obj.b.push(obj.c);obj.c.j = obj.b;b:["a","f",{h:20,j:[]}],c:{h:20,j:["a","f",[]]}function deepClone1(target) {    //通過數(shù)組創(chuàng)建JSON格式的字符串    let str = JSON.stringify(target);    //將JSON格式的字符串轉(zhuǎn)換為JS數(shù)據(jù)    let data = JSON.parse(str);    return data;}

//map存放已經(jīng)拷貝過的對象，key為需要拷貝的對象，value為拷貝后的對象function deepClone(target,map=new Map()){//1.判斷是否是引用類型if(typeof target === "object" && target !==null ){if(map.has(target))return map.get(target); //說明已經(jīng)拷貝過了let isArr = Array.isArray(target);let res = isArr?[]:{};map.set(target,res)if(isArr){//拷貝的是數(shù)組target.forEach((item,index) => {res[index] = deepClone(item,map);});}else{//拷貝的是對象Object.keys(target).forEach(key=>{res[key]=deepClone(target[key],map);})} return res; //返回的是一個數(shù)組或?qū)ο髛else{return target;}}//測試console.log(deepClone([1,[1,2,[3,4]]]))