JSON数据,字段
web前端-js教程
如何判断传过来的JSON数据中，某个字段是否存在，益智游戏源码下载,ubuntu没有根目录,简单用爬虫软件,平板 php,长沙seo网络lzw
1.obj[“key”] != undefined一元购wap源码载,ubuntu命令编写系统,python爬虫点击触发,php 地址,常德seo学校lzw
这种有缺陷，如果这个key定义了，并且就是很2的赋值为undefined，那么这句就会出问题了。代挂源码购买,Ubuntu18缩放,重启虚拟机的tomcat,爬虫扫域名,php管理员登录,研究谷歌seolzw
2.!(“key” in obj)3.obj.hasOwnProperty(“key”)
这两种方法就比较好了，推荐使用。
答案原文：
Actually, checking for undefined-ness is not an accurate way of testing whether a key exists. What if the key exists but the value is actually undefined?
var obj = { key: undefined };
obj[“key”] != undefined // false, but the key exists!
You should instead use the in operator:
“key” in obj // true, regardless of the actual value
If you want to check if a key doesn’t exist, remember to use parenthesis:
!(“key” in obj) // true if “key” doesn’t exist in object
!”key” in obj // ERROR! Equivalent to “false in obj”
Or, if you want to particularly test for properties of the object instance (and not inherited properties), usehasOwnProperty:
obj.hasOwnProperty(“key”) // true