javascript does key exist
var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // falsejavascript does key exist
var person={"name":"Billy","age":20}
person.hasOwnProperty("name"); // true
person.hasOwnProperty("sex"); // falsejavascript check if key exists in object
"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), use hasOwnProperty:
obj.hasOwnProperty("key") // truecheck if a key exists in an object javascript
"key" in obj // true, regardless of the actual valuehow to check if a key exists in an object javascript
!("key" in obj) // true if "key" doesn't exist in object
!"key" in obj // ERROR! Equivalent to "false in obj"js check if object key exists
var obj = { key: undefined };
obj["key"] !== undefined // false, but the key exists!Copyright © 2021 Codeinu
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