欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  web前端

JS中如何判断传过来的JSON数据中是否存在某字段_javascript技巧

程序员文章站 2022-04-15 15:19:06
...
如何判断传过来的JSON数据中,某个字段是否存在,

1.obj["key"] != undefined

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。

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

相关标签: JSON数据 字段