属性简单表达
//属性名
var name = "LiuYashion"
var people = {name} // people { name:"LiuYashion" }
function f(name, locate){
return {name, locate}
}
f("LiuYashion","Shenzhen")
// { name:"LiuYashion", locate:"ShenZhen" }
//方法
var birth = '2000/01/01';
var Person = {
name: 'LiuYashion',
birth, //等同于birth: birth
hello() { console.log('my name is :', this.name); }// 等同于hello: function ()...
};
属性名表达式
let propKey = 'age';
let person = {
[propKey]: 18,
['is' + 'Male']: true,
['say'+'something'](){ console.log( this.age ) }
};//{ age:18, isMale:true }
person.saysomething() // 18
对象做属性名时
//keyA和keyB都转成[object object],需要注意
const keyA = {a: 1};
const keyB = {b: 2};
const myObject = {
[keyA]: 'valueA',
[keyB]: 'valueB'
};
myObject // Object {[object Object]: "valueB"}
对象比较
Object.is('foo', 'foo')
// true
Object.is({}, {})
// false
+0 === -0 //true
NaN === NaN // false
Object.is(+0, -0) // false
Object.is(NaN, NaN) // true
Object.assign()
Object.assign拷贝的属性是有限制的：
- 只拷贝源对象的自身属性（不拷贝继承属性）
- 也不拷贝不可枚举的属性（enumerable: false）
var people = { name:'Liu' }
var age = { age:20 }
var locate = {
domicile:'ShenZhen',
home:{
province:'Hubei',
city:'YiChang'
}
}
var people = Object.assign(people, age, locate)
Object.defineProperty(people, 'invisible', {
enumerable: false,
value: 'hello'
})
console.log( Object.keys(people) )
//[ 'name', 'age', 'domicile', 'home' ]，keys只会遍历可枚举属性
console.log( Object.getOwnPropertyNames(people) )
//[ 'name', 'age', 'domicile', 'home', 'invisible' ]，getOwnPropertyNames可遍历到不可枚举属性
Object.assign方法实行的是浅拷贝，而不是深拷贝。也就是说，如果源对象某个属性的值是对象，那么目标对象拷贝得到的是这个对象的引用。
//locate.home.city改变,people里的键值也改变
locate.home.city = 'XiaoXiTa'
console.log(people)
/*
{
name: 'Liu',
age: 20,
domicile: 'ShenZhen',
home: {
province: 'Hubei',
city: 'YiChang'
}
}
*/
tips
var v1 = 'abc';
var v2 = true;
var v3 = 10;
//文档
var obj = Object.assign({}, v1, v2, v3);
console.log(obj); // { "0": "a", "1": "b", "2": "c" }
var strObj2 = Object('abc')
console.log( strObj2 ) // { "0": "a", "1": "b", "2": "c" }
//实测
var strObj1 = Object("LiuYaXiong")
console.log( strObj1 ) //[String: 'LiuYaXiong']
//Object.assign可以用来处理数组，但是会把数组视为对象。
var strObj3 = Object.assign([1, 2, 3], [4, 5])
console.log( strObj3 )
// [4, 5, 3]
对象的可枚举属性
let objtest = { foo: 123 }
var dis = Object.getOwnPropertyDescriptor(objtest, 'foo')
{
value: 123,
writable: true,
enumerable: true,
configurable: true
}
Object.keys(),Object.values(),Object.entries(),同名方法类似数组
let {keys, values, entries} = Object;
let obj5 = { a: 1, b: 2, c: 3 };
for (let key of keys(obj5)) {
console.log(key); // 'a', 'b', 'c'
}
for (let value of values(obj5)) {
console.log(value); // 1, 2, 3
}
for (let [key, value] of entries(obj5)) {
console.log([key, value]); // ['a', 1], ['b', 2], ['c', 3]
}
对象的扩展运算符类似数组的
Null 传导运算符
var student = {
name:'Nick',
age:18,
hometown:{
province:'GuangDong',
city:'ShenZhen'
}
}
const result = student?.name
console.log(result)
