'Javascript !undefined gives true?
When I try to alert a negation of variable having undefined value , I get the output as true?
alert(undefined);
alert(!undefined);
The first alert gives undefined and second alert gives true.
Is this the expected behavior. If so then why ?Am I missing some concept/theory about undefined in Javascript?
Solution 1:[1]
Yes, it is the expected behavior.
Negation of the following values gives true in javaScript:
- false
- undefined
- null
- 0 (number zero)
- ""(empty string)
eg: !undefined = true
Note: The following checks return true when you == compare it with false, but their negations will return false.
- " "(space only).
- [ ](empty array),
eg: [ ] == false gives true, but ![ ] gives false
Solution 2:[2]
Sources
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Source: Stack Overflow
| Solution | Source |
|---|---|
| Solution 1 | |
| Solution 2 | Digger2000 |