Is there any difference in using !! vs using checks for null | undefined? in javascript/typescript

Question

I was wondering if there is any difference when using ! vs checks like isNullOrUndefined or even custom checks like

customIsNullOrUndefined(obj: any) { return obj === null || obj === undefined;}

vs

!obj

vs

util.isNullOrUndefined(obj)

I know that util.isNullOrUndefined is deprecated

I mean semantically !obj should return the same as the checks for null | undefined

Answer 1

!obj will evaluate to true for any falsy value . That means null or undefined , but also things like 0 or "" . You can use this if you're sure you're only checking objects and not primitive values.

Answer 2

The not operator of ! determines whether a value is falsy, which includes the following:

• false
• 0
• undefined
• null
• ''

If a function checks for null or undefined , then it will not check for other falsy values, such as false , for example.