Why does javascript's "in" operator return true when testing if 0 exists in an array that doesn't co

Posted by Mariano Peterson on Stack Overflow See other posts from Stack Overflow or by Mariano Peterson
Published on 2010-06-18T03:40:02Z Indexed on 2010/06/18 3:43 UTC
Read the original article Hit count: 335

Filed under:

JavaScript

|

array

|

operator

For example, this returns true, and makes sense: var x = [1,2]; 1 in x; // true

This returns false, and makes sense: var x = [1,2]; 3 in x; // false

However this returns true, and I don't understand why: var x = [1,2]; 0 in x;

You can quickly test it by putting this in your browser's address bar: javascript:var x=[1,2]; alert(0 in x);

Why does the "in" operator in Javascript return true when testing if "0" exists in array, even when the array doesn't appear to contain "0"?

© Stack Overflow or respective owner

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

Related posts about array

Array reverse and Array sort on One int array and store into another array using delgate

as seen on Stack Overflow - Search for 'Stack Overflow'
Array reverse and Array Sort on an int array and store into another array using a delegate. We have to accept the elements from the user >>> More
LWJGL Voxel game, glDrawArrays

as seen on Game Development - Search for 'Game Development'
I've been learning about 3D for a couple days now. I managed to create a chunk (8x8x8). Add optimization so it only renders the active and visible blocks. Then I added so it only draws the faces which don't have a neighbor. Next what I found from online research was that it is better to use glDrawArrays… >>> More
Sorting a Multidimensional array...

as seen on Stack Overflow - Search for 'Stack Overflow'
I need to sort an array that can look like this: $array[4][0] = array('id' => 1, 'value' => 2); $array[3][2] = array('id' => 0, 'value' => 3); $array[4][1] = array('id' => 1, 'value' => 0); $array[1][3] = array('id' => 2, 'value' => 1); $array[1][1] = array('id' => 3, 'value'… >>> More
why i add more insignificant code but cost less time

as seen on Stack Overflow - Search for 'Stack Overflow'
i write a method and when i add some insignificant code it works faster, like these : array[1]=array[1]; array[0]=array[0]; array[3]=array[3]; array[2]=array[2]; i use double t=System.currentTimeMillis(); at first to record the time. then call the method and use System.out.println(System.currentTimeMillis()-t);… >>> More
Difference between array('Acl' => array('type' => 'requester')) and array('Acl' => 'requester') in C

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm following the ACL tutorial for CakePHP 1.3 and I was wondering if there is a functional difference between declaring a behavior like this: var $actsAs = array('Acl' => 'requester'); and like this: var $actsAs = array('Acl' => array('type' => 'requester')); >>> More