JavaScript Discussion Boards

Condition Always true when checking for "undefined" in Javascript

Vimalsoft(Pty) Ltd3-Aug-14 9:28

3-Aug-14 9:28

Good Day all

i am reluctantly maintaining a Classic Asp application that will be re-written in few months to come. i have an issue where i have a Code like this

if(document.frmEntry.optMethod != "undefined")
                    {
                        if (document.frmEntry.optMethod.selectedIndex == 0) {
                            strPrompt=strPrompt+'Please specify the Valuation Method\n';
                            if ( objFocus == null ) {
                                objFocus = document.frmEntry.optMethod;
                            }
                        }
                    }

my problem here is that even if document.frmEntry.optMethod is not equal to "undefined" the code still go into the condition as if it was true. i have attached a proof in my debuger.

http://www.vetauinvest.com/Example/IE_DEBUGGER.png[^]

Thanks

Vuyiswa Maseko,

Spoted in Daniweb-- Sorry to rant. I hate websites. They are just wierd. They don't behave like normal code.

C#/VB.NET/ASP.NET/SQL7/2000/2005/2008
http://www.vuyiswamaseko.com
vuyiswa[at]dotnetfunda.com
http://www.Dotnetfunda.com

modified 3-Aug-14 15:47pm.

Re: Condition Always true when checking for "undefined" in Javascript

Blikkies3-Aug-14 22:48

Blikkies

3-Aug-14 22:48

Try using a Falsy check.

The following values are always falsy:

false
0 (zero)
"" (empty string)
null
undefined
NaN (a special Number value meaning Not-a-Number!)

Your code should look like as follows:

JavaScript

if(!document.frmEntry.optMethod)
                       {
                           if (document.frmEntry.optMethod.selectedIndex == 0) {
                               strPrompt=strPrompt+'Please specify the Valuation Method\n';
                               if ( objFocus == null ) {
                                   objFocus = document.frmEntry.optMethod;
                               }
                           }
                       }

Re: Condition Always true when checking for "undefined" in Javascript

Kornfeld Eliyahu Peter4-Aug-14 0:19

Kornfeld Eliyahu Peter

4-Aug-14 0:19

You are very true about 'false' check, but sometimes it is a good practice to write full code and explicitly state against what are you want to check. It's of course only a matter of maintainability/readability...

I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is. (V)

Re: Condition Always true when checking for "undefined" in Javascript

Kornfeld Eliyahu Peter3-Aug-14 22:55

Kornfeld Eliyahu Peter

3-Aug-14 22:55

That should be undefined and NOT "undefined"!!!

I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is. (V)

Re: Condition Always true when checking for "undefined" in Javascript

Graham Breach3-Aug-14 22:56

Graham Breach

3-Aug-14 22:56

The "undefined" shown in the debugger is not a string, so you can't compare it as one.

To really test if your value is undefined, you can use this:

JavaScript

if(typeof document.frmEntry.optMethod != 'undefined')

The typeof operator returns the type of the argument as a string.

Re: Condition Always true when checking for "undefined" in Javascript

Kornfeld Eliyahu Peter4-Aug-14 0:15

Kornfeld Eliyahu Peter

4-Aug-14 0:15

I can't see why use undefined as string - with or without typeof!?
In JavaScript undefined is a value property of the global namespace and yous should use it according to it...

I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is. (V)

Re: Condition Always true when checking for "undefined" in Javascript

Vimalsoft(Pty) Ltd4-Aug-14 5:39

Vimalsoft(Pty) Ltd

4-Aug-14 5:39

Thank you , this info is enough to solve the issue.

thanks again

Re: Condition Always true when checking for "undefined" in Javascript

Graham Breach4-Aug-14 9:18

Graham Breach

4-Aug-14 9:18

The typeof for an undefined value is always "undefined". The value undefined being in the global namespace opens up some possible problems:

JavaScript

function madness() {
  // override with local variable
  var a = 'fish', undefined = 'fish';

  if(a === undefined) {
    // both 'fish', so here we are
  }
}

function mistake() {
  var a = 'fish';

  // common mistake, using '=' instead of '=='
  if(undefined = a) {
    // 'undefined' is not a constant or keyword, so the whole 
    // expression is valid and will be true
  }
}

I know these are pretty unlikely scenarios, but better safe than sorry.

In earlier browsers "undefined" was not a testable value so expressions like (a == undefined) would produce the helpful message "undefined is undefined".

Re: Condition Always true when checking for "undefined" in Javascript

Kornfeld Eliyahu Peter4-Aug-14 18:38

Kornfeld Eliyahu Peter

4-Aug-14 18:38

Graham Breach wrote:
The typeof for an undefined value is always "undefined".

How that?

JavaScript

var undefined = 'fish';
alert(typeof undefined); // string!!!

I'm not questioning your powers of observation; I'm merely remarking upon the paradox of asking a masked man who he is. (V)

Re: Condition Always true when checking for "undefined" in Javascript

Graham Breach4-Aug-14 22:13

Graham Breach

4-Aug-14 22:13

Yes. If you define undefined as a string variable, then it is no longer undefined and things get confusing.

This is why I was testing the type of the value against the string "undefined" - the string is a constant.

Re: Condition Always true when checking for "undefined" in Javascript

Tushar Guru8-Sep-14 21:59

Tushar Guru

8-Sep-14 21:59

You can try with remove ("") double quotes OR use ('') single quotes.

modified 9-Sep-14 7:56am.

Newbie Question On jQuery Selectors

Richard Andrew x641-Aug-14 17:03

Richard Andrew x64

1-Aug-14 17:03

I'm reading a tutorial about using selectors in jQuery to modify items on the page. I understand most of it, except I can't figure out why the first line of code below uses a comma to separate the selectors, and the second code line does not. Can anybody tell me when the comma is used and when not?

$('footer, header').slideUp('slow').slideDown('slow'); // Grouped
$('#Sidebar img').fadeTo(5000, 0.1); // Combined

The difficult we do right away...
...the impossible takes slightly longer.

Re: Newbie Question On jQuery Selectors

thatraja1-Aug-14 18:09

thatraja

1-Aug-14 18:09

Line1 - jQuery multiple elements Selector[^]
Line2 - jQuery parent descendant Selector[^]

One more similar selector - jQuery mulitple classes Selector[^]
FYI jQuery Selectors[^]

thatraja

Code converters | Education Needed | Improve Everything^New

Re: Newbie Question On jQuery Selectors

Richard Andrew x641-Aug-14 18:28

Richard Andrew x64

1-Aug-14 18:28

Thank you. Smile | :)

The difficult we do right away...
...the impossible takes slightly longer.

Generate geofence for route (pointA to pointB)

JANANDOJAN28-Jul-14 21:19

JANANDOJAN

28-Jul-14 21:19

I'm working on a task where given the coordinates of a line from point A to point B, I need to create a polygonal geofence around(50meters) this line (road route) in google maps.
Can some one help with this?

Re: Generate geofence for route (pointA to pointB)

JANANDOJAN29-Jul-14 23:02

JANANDOJAN

29-Jul-14 23:02

I found the solution...
https://coderwall.com/p/zb_zdw[^]

Re: Generate geofence for route (pointA to pointB)

Kwod128-Dec-20 11:01

Kwod12

8-Dec-20 11:01

omg ty so much

Using json and jquery on page not working

Member 1094998624-Jul-14 8:36

Member 10949986

24-Jul-14 8:36

XML

Please, I am using two javascript files, which has its own assigned worked, on a php page, however the jquery script stops working while the JSON2 script works.
This is how I implement both on the php page

    <script type="text/javascript" src="jquery.min.js" ></script>
    <script type="text/javascript" src="JSON2.js" ></script>

The link to the jquery file http://code.jquery.com/jquery-1.11.1.min.js

The link to JSON2.js :
https://raw.githubusercontent.com/douglascrockford/JSON-js/master/json2.js

**Question**

 Please, is it possible to use both script on the same page? if yes, please how to I go about it?

Thanks for helping.

Re: Using json and jquery on page not working

ZurdoDev24-Jul-14 10:07

ZurdoDev

24-Jul-14 10:07

I'm unaware of any issues using the 2 together. It would help if you could tell us what is happening.

There are only 10 types of people in the world, those who understand binary and those who don't.

Re: Using json and jquery on page not working

Member 1094998624-Jul-14 11:14

Member 10949986

24-Jul-14 11:14

This is what i see in my web console log

SyntaxError: JSON.parse: unexpected character , this is found in th json.js

TypeError: Q[a].exec is not a function , this is also found in the jquery.js

Re: Using json and jquery on page not working

ZurdoDev24-Jul-14 11:40

ZurdoDev

24-Jul-14 11:40

Does your code have errors?

There are only 10 types of people in the world, those who understand binary and those who don't.

Re: Using json and jquery on page not working

Member 1094998624-Jul-14 11:50

Member 10949986

24-Jul-14 11:50

Hi, i think i have solved it,I was previously using json and now i have to changed it to json2

disable a onclick function, and enable it

jkirkerx18-Jul-14 12:24

jkirkerx

18-Jul-14 12:24

I have this list of items in a div container, so each item has it's own container. It's a long list of previous orders, a ticket list on the left.

You can click on the container, and the background-color will change, and it will fire a function that accesses a web service, and create a ticket for the item on the right.

LEFT SIDE | RIGHT SIDE
ORDERS | ORDER TICKET PREVIEW

I want to disable the click on the left, the orders, while the ticket on the right is created, so dumb users don't click the thing to death.

I'm not sure how to go about this one, looking for ideas. I wrote it in Javascript, with a little jQuery mixed in.
I was looking for a neat clean way to do this, without globals and chopping it up. I can't see how I can recreate the complex onclick to enable it again, and don't understand what happens to the vars I pass.

Perhaps I can somehow disable the whole container from the click, preserving the underlying click.

So this runs in a for loop, and creates a container for each previous order, with order data inside it.

Hope I was able to convey my thoughts here clearly.

function build COH_List() {
 var div_item_container = document.createElement('div');
 div_item_container.id = m_ID;
 div_item_container.className = 'div_item_container';
 div_item_container.style.width = '100%';
 div_item_container.style.height = '42px';
 div_item_container.style.margin = '3px 0px';
 div_item_container.style.borderBottom = "dotted 1px rgb(200,200,200)";
 div_item_container.style.display = 'block';
 div_item_container.style.cssFloat = 'clear';
 div_item_container.onclick = (function (m_ID, m_orderID, m_orderNumber, m_orderDate) { return function () { select_order_click(m_ID, m_orderID,    m_orderNumber, m_orderDate); }; })(m_ID, m_orderID, m_orderNumber, m_orderDate);
div_items_container.appendChild(div_item_container);

And then I have a function below that builds the order ticket.

function load_orderDetails() {
  // when this runs, disable the onclick in the function above.

}

Re: disable a onclick function, and enable it

Dennis E White29-Jul-14 4:04

Dennis E White

29-Jul-14 4:04

have you tried...

JavaScript

element.onclick = '';

maybe write your handler like so.

JavaScript

function load_orderDetails(ele) {
    ele.onclick = '';

    // do your work here for loading whatever
}

just make sure when you call it you pass it the element that you want disabled. just by chance are you using jQuery because there are message handlers that will do this for you??

Re: disable a onclick function, and enable it

jkirkerx29-Jul-14 6:01

jkirkerx

29-Jul-14 6:01

I'll give that that a try later today. Good Idea!
Will let you know the outcome.

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