When is (true == x) === !!x false?

Posted by Paul S. on Stack Overflow See other posts from Stack Overflow or by Paul S.
Published on 2012-11-25T16:57:36Z Indexed on 2012/11/25 17:04 UTC
Read the original article Hit count: 154

Filed under:

JavaScript

JavaScript has different equality comparison operators

Equal ==
Strict equal ===

It also has a logical NOT ! and I've tended to think of using a double logical NOT, !!x, as basically the same as true == x.

However I know this is not always the case, e.g. x = [] because [] is truthy for ! but falsy for ==.

So, for which xs would (true == x) === !!x give false? Alternatively, what is falsy by == but not !! (or vice versa)?

Related posts about JavaScript

CHAT ROOMs 7 by 6

as seen on Stack Overflow - Search for 'Stack Overflow'
I am looking for chatroom on one page with 7 loggedin users and 6+rows for say 42 users.these users will keep on adding wthnew users.Need urgent help.A PRETTY UNUSUAL Q FOR MOST OF U.What is MORE REQ new features: Usernames are unique to users currently chatting You can see a "currently chatting"… >>> More
Integrating JavaScript Unit Tests with Visual Studio

as seen on Stephen Walter - Search for 'Stephen Walter'
Modern ASP.NET web applications take full advantage of client-side JavaScript to provide better interactivity and responsiveness. If you are building an ASP.NET application in the right way, you quickly end up with lots and lots of JavaScript code. When writing server code, you should be writing… >>> More
Has Javascript developed beyond what it was originally designed to do?

as seen on Programmers - Search for 'Programmers'
I've been talking with a friend about the purpose of Javascript, when and how it should be used, etc. He quoted that: JavaScript was designed to add interactivity to HTML pages [...] JavaScript gives HTML designers a programming tool HTML authors are normally not programmers… >>> More
PHP, javascript, single quote problems with IE when passing variable from ajax post to javascript fu

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi! I have been trying to get this to work for a while, and I suspect there's an easy solution that I just can't find. My head feels like jelly and I would really appreciate any help. My main page.php makes a .post() to backend.php and fetches a list of cities which it echoes in the form of: <li… >>> More
Javascript in XSL that is loaded by Javascript

as seen on Stack Overflow - Search for 'Stack Overflow'
Is there anyway to have javascript run when a XSL sheet has been applied to an XML file by Javascript? I am using a JQuery plugin to apply the sheet to the xml but the javascript that is located inside of the XSL file will not run. I put the Javascript at the bottom of the file and it still does… >>> More

Developer IT

When is (true == x) === !!x false? - Developer IT

When is (true == x) === !!x false?

JavaScript

Related posts about JavaScript

CHAT ROOMs 7 by 6

Integrating JavaScript Unit Tests with Visual Studio

Has Javascript developed beyond what it was originally designed to do?

PHP, javascript, single quote problems with IE when passing variable from ajax post to javascript fu

Javascript in XSL that is loaded by Javascript

Categories cloud