//获取视窗高度
        let htmlWidth = document.documentElement.clientWidth || document.body.clientWidth;
        //获取html
        let htmlDom = document.getElementsByTagName('html')[0]
        //rem的基准值
        htmlDom.style.fontSize = htmlWidth / 10 + 'px'

       var _a = 0,
            _b = 0;
        function A(_a) {
            A = function (_b) {
                alert(_a + _b++)
            }
            alert(_a++)
        }
        A(1) 
        A(2) 

 var _a = 0,_b = 0
    function A(_a) { //1.执行A(1),_a=1
        A = function (_b) {//2. 在执行完A(1),A以后的赋值指向这里
            alert(_a + _b++)// _a + _b++=1 (_b++，先运算后赋值)
        }
        alert(_a++)//执行_a++先运算后赋值，下次使用时_a=2
    }
    A(1) //1
    A(2) //4 执行function(_b),此时没有a的值，在作用域上下文里找_a=2,执行_a+_b++=2+2=4

 let obj = {
            a: 100,
            b: [10, 20, 30],
            c: { x: 10 },
            d: /^\d+$/
        }

        //浅克隆
        let obj1 = {}
        for (let key in obj) {
            if (!obj.hasOwnProperty(key)) break;
            obj1[key] = obj[key]
        }
        obj1.c.x = 444
        console.log("obj1", obj1)
        console.log("obj", obj)// obj1.c.x = 444后obj.c.x也会变成444

        //深克隆
        let obj3 = JSON.parse(JSON.stringify(obj)) //函数和正则在被JSON.stringify后都会变成{},new Date会变成字符串
        //递归
        console.log("obj3", obj3)
function deepClone(obj) {
            //如果是空直接返回null
            if (obj == 'null') return null
            //如果不是对像，则返回对应值
            if (typeof obj !== 'object') return obj
            //如果是正则则返回新的正则,或者使用Object.prototype.toString.call()判断类型值
            if (obj instanceof RegExp) {
                return new RegExp(obj)//创建新实例,高出新地址
            }
            if (obj instanceof Date) {
                return new Date(obj)
            }
            //不直接创建空对象的目的；克隆的结果和之前的保持相同的所属类
            let objClone = new obj.constructor
            for (let key in obj) {
                if (obj.hasOwnProperty(key)) {
                    objClone[key] = deepClone(obj[key]);//（如果是函数、对象）需递归，其他不需要
                }
            }
            return objClone
        }
        let objDeep = deepClone(obj)
        objDeep.c.x = 666
        console.log("objDeep", objDeep)
        console.log("obj", obj)

 var a=?
 if (a == 1 && a == 2 && a == 3) {
    console.log('a == 1 && a == 2 && a == 3');
 }

 var a = {
            i: 0,
            toString() {
                return ++this.i
            }
        }
 if (a == 1 && a == 2 && a == 3) {
            console.log('a == 1 && a == 2 && a == 3');
 }

   var i = 0
   Object.defineProperty(window, 'a', {
       //get不能再次获取当前属性
       get() {
   return ++i
       }
   })
   if (a == 1 && a == 2 && a == 3) {
       console.log('a == 1 && a == 2 && a == 3');
   }

    //数组解决
    var a = [1, 2, 3]
    a.toString = a.shift
    if (a == 1 && a == 2 && a == 3) {
        console.log('a == 1 && a == 2 && a == 3');
    }

        function Foo() {
        getName = function () {
            console.log(1);

        }
        return this
        }
        Foo.getName = function () {
            console.log(2);
        }
        Foo.prototype.getName = function () {
            console.log(3);
        }
        var getName = function () {
            console.log(4);
        }
        function getName() {
            console.log(5)
        }
        Foo.getName()
        getName()
        Foo().getName()
        getName()
        new Foo.getName()
        new Foo().getName()
        new new Foo().getName()

        async function async1() {
            console.log('async1 start')
            await async2()
            console.log('async1 end')
        }
        async function async2() {
            console.log('async2')
        }
        console.log('script start');
        setTimeout(function () {
            console.log('setTimeout');
        }, 0);
        async1()
        new Promise(function (resolve) {
            console.log('promise1');
            resolve()
        }).then(function () {
            console.log('promise2');
        })
        console.log('script end');