JS中判斷JSON資料是否存在某欄位的方法_javascript技巧

如何判斷傳過來的JSON資料中，某個欄位是否存在，

1.obj["key"] != undefined
這種有缺陷，如果這個key定義了，而且就是很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 ally the value 🎜>var obj = { key: undefined };
obj["key"] != undefined // false, but the key exists!

You should instead use the in operator:

You should instead use the in operator:

You should instead use the in operator:

You should instead use the in operator:

You should instead use the in operator:

You should instead use the in operator:

You should instead use the in operator:
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 // ERROR! Equivalent to "false in obj" Or, if you want to particularly want to particularly test for properties of the object instance (and not inherited properties), usehasOwnProperty: obj.hasOwnProperty("key") // true