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JS中判斷JSON數據是否存在某字段的方法

  這篇文章主要介紹了JS中如何判斷JSON數據是否存在某字段,需要的朋友可以參考下

  如何判斷傳過來的JSON數據中,某個字段是否存在,

  1.obj["key"] != undefined

  這種有缺陷,如果這個key定義了,並且就是很2的賦值為undefined,那麼這句就會出問題了。

  2.!("key" in obj)

  3.obj.hasOwnProperty("key")

  這兩種方法就比較好了,推薦使用。

  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

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