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??

???JavaScript?????????????????????????????????????????????????????????????????????????????????????

????

1.?????

var empty={} //???????

var obj={a:1,b:2};//??????? var compObj={a:'1',b:'2',cc:{d:'3',e:'4'}};//?????

2.new???????????

var a = new Array();//???????

var d = new Date();//???????Date??

3.??????

function Person(name){this.name=name;}

Person.prototype.eat=function(){console.log(this.name+"????");} var zhangsan = new Person("??");

4.Object.create()

var o1=Object.create({a:1,b:2});//o1????? a?b

????????

?????(.)????([])???????

var o1={a:1,b:2,'hello zhangsan':'??'}

o1.a //1 o1.b //2 o1['a']//1 o1['b']//2 var key='hello zhangsan'; o1[key]//?? o1.key//undefined o1.hello zhangsan //??

??? (.) ?????????????????????????????????????????????????????????????????

??????????????????

o1.a='3'

o1['b']='4'

????

delete o1.a; delete o1['b']

???delete?????????????????????

????

1.in???

'a' in o1;//true

'b' in o1;//true 'toString' in o1;//true

2.hasOwnPreperty()??

o1.hasOwnProperty('a');//true

o1.hasOwnProperty('b');//true o1.hasOwnProperty('toString');//false

3.?? !==undefined

o1.a!==undefined;//true

o1.b!==undefined;//true o1.toString!==undefined;// ???????true

??????????undefined????????????? var o1={a:undefined} ,??a????????????

?????

1.for/in??

for(key in o1){console.log(key,'===',o1[key])}

2.Object.keys ??

var keys = Object.keys(o1);

keys.forEach((key)=>{console.log(key,'===',o1[key])}

????

???__proto__??????????prototype?

prototype??constructor ??????????? isPrototypeOf?????????????????????????????

?????

1.valueOf() ????????????

Array?????????

var array = [1,3,4,6];console.log(array.valueOf() === array); // true Number?????? var num = 123213;console.log(num.valueOf()); // 15.2654 boolean??????true?false var bool = true;console.log(bool.valueOf() === bool); // true

2.toString() ???????????????

?????????????????????

var toString = Object.prototype.toString; console.log(toString.call(new Object()));//[object Object] console.log(toString.call(new Date())); // [object Date] console.log(toString.call('abc')); // [object String] console.log(toString.call(123)); // [object Number] console.log(toString.call(true)); // [object Boolean] console.log(toString.call(undefined)); // [object Undefined] console.log(toString.call(null)); // [object Null] console.log(toString.call(/./));//[object RegExp]

3.toLocaleString() ???????????????

var toString = Object.prototype.toLocaleString; console.log(toString.call(new Object()));//[object Object]

console.log(toString.call(new Date())); // Wed Dec 23 2020 20:09:24 GMT+0800 (??????) console.log(toString.call('abc')); // abc console.log(toString.call(123)); // 123 console.log(toString.call(true)); // true console.log(toString.call(/./));// /./

4.hasOwnProperty() ??????????

var o1={a:1,b:2,'hello zhangsan':'??'}

console.log(o1.hasOwnProperty('a'));//true console.log(o1.hasOwnProperty('b'));//true console.log(o1.hasOwnProperty('toString'));//false

5.propertyIsEnumerable() ??

var o1={a:1,b:2,'hello zhangsan':'??'}

console.log(o1.propertyIsEnumerable('a'));//true console.log(o1.propertyIsEnumerable('b'));//true console.log(o1.propertyIsEnumerable('toString'));//false

6.isPrototypeOf() ??

function Person(){}

function Man(){} Man.prototype = Object.create(Person.prototype); var m = new Man(); console.log(Person.prototype.isPrototypeOf(m)); // true console.log(Object.prototype.isPrototypeOf(m)); // true

???????? m ?????__proto__???Person.prototype?????Person.prototype???__proto__?????Object.prototype???