Preferred way to check object property is `null` or `undefined`

Question

If I have some object that has a property that may or may not exist, is there a preferred way to check for its' existence?

// Good?
(someObj.property !== undefined && someObj.property !== null)

// Better?
(typeof someObj.property !== 'undefined')

// Best?
(someObj.property != null)

*The last != operator is on purpose:

Strict equality checks (===) must be used in favor of abstract equality checks (==). The only exception is when checking for undefined and null by way of null. The use of == null is also acceptable in cases where only one of null or undefined may be logically encountered, such as uninitialized variables.

The first and the last are equivalent. The middle one won't check `null` values. So first it depends on what you want. Then it depends on how much you want to type ;) Whether or not to use `!= null` is a personal preference. — Felix Kling, Jun 06 '17 at 15:52

Adam Hartleb · Answer 1 · 2017-06-06T16:00:54.307

0

I reckon you'd use obj.hasOwnProperty(prop)

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty

edited Jun 06 '17 at 16:00

answered Jun 06 '17 at 15:54

Adam Hartleb

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Depends on whether `null` values should be considered or not. – Felix Kling Jun 06 '17 at 15:57
Please provide more details for your link. Check out [answer] for more details. – Tim Hutchison Jun 06 '17 at 16:01
Wouldn't that be checking for the value of the property and not whether the property itself exists? – Adam Hartleb Jun 06 '17 at 16:02

Preferred way to check object property is `null` or `undefined`

1 Answers1