September 2022
Intermediate to advanced
585 pages
8h 17m
Chinese
Content preview from JavaScript 经典实例：第三版
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180
｜
第
7
章
表
7
-
1
：查找对象属性的不同方式
方法
返回值
获取可枚
获取不可
获取符号
包括继承
举的属性
枚举的属性
属性
的属性
Object.keys()
属性名称数组
是
否
否
否
Object.values()
属性值数组
是
否
否
否
Object.entries()
属性数组构成的数组
，
是
否
否
否
每个属性数组中包含属
性的名称和对应的值
Object.getOwnProperty
属性名称数组
是
是
否
否
Names()
Object.getOwnProperty
属性名称数组
否
否
是
否
Symbols()
Object.getOwnProperty
属性描述符对象数组
，
是
是
是
否
Descriptors()
类似于
defineProperty()
使用的那种
（
7.7
节
）
Reflect.ownKeys()
属性名称数组
是
是
是
否
for...in
循环
每个属性名称
是
否
否
是
7.4.4
参考
7.3
节介绍如何使用
in
运算符检查单个属性。
7.5
测试空对象
7.5.1
问题
你想判断一个对象是否为空（没有属性）。
7.5.2
方案
使用
Object.keys()
方法获取属性数组，检查数组的
length
是否为
0
。
const
blankObject = {};
if
(Object.keys(blankObject).length === 0) {
//
这里的代码将运行，因为该对象中什么也没有
对象
｜
181
}
const
objectWithProperty ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.