473,699 Members | 2,278 Online
Bytes | Software Development & Data Engineering Community
+ Post

Home Posts Topics Members FAQ

Help: Program flow when error in onclick event?

I was wondering,

what happens when you have an onclick event and an error occurs in it:

In an <a> element:
onclick="zoomFu llExtent(); return false;"

I know that there is an error happening in zoomFullExtent. I didn't
define my own error handler, so the default one is used.(My browser is
Firefox 1.0).

I notice that when this error happens, the browser makes a request to
the server.
I thought that if an error happened in zoomFullExtent, the default
error handler would catch it, and then zoomFullExtent would return
normally. But that doesn't seem to happen. Instead the whole onclick
script returns or is aborted? And it seems to return true so that the
request is made. Is there a page where this program flow is explained?

Thanks for reading,

Roland
Jul 23 '05 #1
4 1961
Lee
Roland said:

I was wondering,

what happens when you have an onclick event and an error occurs in it:

In an <a> element:
onclick="zoomF ullExtent(); return false;"

I know that there is an error happening in zoomFullExtent. I didn't
define my own error handler, so the default one is used.(My browser is
Firefox 1.0).

I notice that when this error happens, the browser makes a request to
the server.
I thought that if an error happened in zoomFullExtent, the default
error handler would catch it, and then zoomFullExtent would return
normally. But that doesn't seem to happen. Instead the whole onclick
script returns or is aborted? And it seems to return true so that the
request is made. Is there a page where this program flow is explained?


It doesn't have to return true. The link is followed unless the onclick handler
specifically returns false. The best solution is probably to avoid using a link
in that case.

Jul 23 '05 #2
Roland wrote:
I was wondering,

what happens when you have an onclick event and an error occurs in it:

In an <a> element:
onclick="zoomFu llExtent(); return false;"

I know that there is an error happening in zoomFullExtent. I didn't
define my own error handler, so the default one is used.(My browser is
Firefox 1.0).

I notice that when this error happens, the browser makes a request to
the server.
I thought that if an error happened in zoomFullExtent, the default
error handler would catch it, and then zoomFullExtent would return
normally. But that doesn't seem to happen. Instead the whole onclick
script returns or is aborted? And it seems to return true so that the
request is made. Is there a page where this program flow is explained?

Thanks for reading,

Roland


Uncaught errors may exit one or more execution contexts - so it is
possible for an error in 'zoomFullExtent ()' to cause your onclick to
exit. If that happens, your onclick will return something other than
'false' and the link will be followed.

Where an onclick is used to intercept the default action of an HTML
element (say an <a href="... ), it is normal for the function to
return an appropriate value that controls whether or not the action
is performed, e.g.

<a href="..." onclick="return zoomFullExtent( );" ...>

and in zoomFullExtent( ):

function zoomFullExtent( ){
var OK = false;

// do some stuff, test that everything works as expected

if ( /* everything OK */ ) {
OK = true;
}
return !OK;
}

This may not suit you in this case though. Look in the ECMA spec
section 10.2.

--
Rob
Jul 23 '05 #3
"...it is normal for the function to return an appropriate value that
controls whether or not the action is performed"

No, actually, with click handlers on buttons and links, returning true
or null will allow the link to be processed as if your click handler
didn't exist. You will almost always want to return false. What you
probably want is something like this:

<a href="#" onclick="return zoomFullExtent( );">link</a>

and in zoomFullExtent( ):
var debug = true;
function zoomFullExtent( ) {
try {
//do your normal stuff
} catch( e ) {
if( debug ) alert( "Error in zoomFullExtent: " + e );
}

return false;
}

Note that the try...catch blocks handle any errors you receive. Setting
debug to false will hide the errors from end users. And, most
importantly, the function always returns false.

Jul 23 '05 #4
Gregory wrote:
"...it is normal for the function to return an appropriate value that
controls whether or not the action is performed"

No, actually, with click handlers on buttons and links, returning true
or null will allow the link to be processed as if your click handler
didn't exist.
Yes, that's exactly what is required in most cases (of course we
speak in terms of our own experience here)
You will almost always want to return false. What you
probably want is something like this:

<a href="#" onclick="return zoomFullExtent( );">link</a>
No, you want the onclick handler to do something and if the
client-side JavaScript does not do it, then the link should head off
to the server where something appropriate happens - either the
functionality is provided server-side or an explanation is given as
to why it didn't happen.

Therefore only if the script does what it's supposed to should
'false' be returned. Any other value causes the link to be followed -
this logic is inherent in the architecture of intrinsic events.

and in zoomFullExtent( ):
var debug = true;
function zoomFullExtent( ) {
try {
//do your normal stuff
} catch( e ) {
if( debug ) alert( "Error in zoomFullExtent: " + e );
}

return false;
}

Note that the try...catch blocks handle any errors you receive. Setting
debug to false will hide the errors from end users. And, most
importantly, the function always returns false.


So if the script errors, nothing useful happens? It also suggests
that all functions called by intrinsic events should have try/catch
blocks. Some of the more learned contributors may wish to comment on
that proposition.
--
Rob
Jul 23 '05 #5

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

9
2409
by: hope | last post by:
Hi Access 97 I'm lost on this code please can you help ================================= Below is some simple code that will concatenate a single field's value from multiple records into a single string separated by a user defined character. There is no error trapping (by design), USE AT YOUR OWN RISK.
1
2751
by: MDBloemker | last post by:
can anyone help me fathom out how to use this bit of code: Public Class Utilities Public Shared Sub CreateConfirmBox(ByRef txt As WebControls.TextBox, _ ByVal strMessage As String) txt.Attributes.Add("onchange", "return confirm('" & strMessage & "');") End Sub End Class
7
1699
by: Tigger | last post by:
Dear Experts, I am working on ASP.NET. I have got a problem related to the usage of Javascript in ASP.NET. Please help. The story is the following: 1) I am developing an ASP.NET application. I need to prompt the users with a modal box (with "Yes" and "Cancel" button on it); 2) When the user clicks "Yes" button, I need to do some further processing. If "Cancel" is clicked, of course, stops doing anything; 3) Now the problems are: -...
11
7754
by: Joe | last post by:
Hello All, I have an ASP.NET page with one Textbox (SearchTextBox) and one ImageButton (SearchButton) server controls. The user can type search text in SearchTextBox and click SearchButton and the web server performs a database query and displays the results. All of this works fine. I want the user to be able to press the Enter key while the cursor is still in SearchTextBox and have the SearchButton.Click event fire (thus performing...
6
1908
by: drec | last post by:
I am just learning Javascript and I would like to create a basic form that gives me two options. This will be using either checkbox or radio input type, however I would like the second option to allow the user to type in a value. Also, I would like the 2nd option only editable if the button for that option is selected. All I can seem to find is basic examples of forms, and none of which have this feature. The form would look something...
19
2203
by: pamelafluente | last post by:
Hi Guys, I am trying to include my little script in my html report. I have done an external JS file which contains it. If you remember, you have helped me to detect if the asp page was present by using ajax. If not present is gracefully stay silent. The problem is now that when the JS is not present (and it can be) MSIE gives a lot of errors and one has to kill it.
0
5569
by: gunimpi | last post by:
http://www.vbforums.com/showthread.php?p=2745431#post2745431 ******************************************************** VB6 OR VBA & Webbrowser DOM Tiny $50 Mini Project Programmer help wanted ******************************************************** For this teeny job, please refer to: http://feeds.reddit.com/feed/8fu/?o=25
5
3692
by: althafexcel | last post by:
hi everyone Im trying to include an external js in my aspx page under the head tag, it doesn't load or it displays an object expected error whenver the function from the .js is called. Actually for repeated html im using the external js, i mean the TOP, BOTTOM they are repeated in every page, so i include them as functions in the external js and call them. Why it doesn't work?
17
2675
by: yawnmoth | last post by:
http://www.frostjedi.com/terra/scripts/demo/this-alert.html http://www.frostjedi.com/terra/scripts/demo/this-alert2.html Why, when you click in the black box, do the alert boxes say different things? Shouldn't they say the same thing?
0
8691
marktang
by: marktang | last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look ! Part I. Meaning of...
0
8620
by: Hystou | last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it. First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
0
9180
Oralloy
by: Oralloy | last post by:
Hello folks, I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>". The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed. This is as boiled down as I can make it. Here is my compilation command: g++-12 -std=c++20 -Wnarrowing bit_field.cpp Here is the code in...
0
8887
tracyyun
by: tracyyun | last post by:
Dear forum friends, With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
0
7755
agi2029
by: agi2029 | last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own.... Now, this would greatly impact the work of software developers. The idea...
1
6536
isladogs
by: isladogs | last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM). In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules. He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms. Adolph will...
0
4378
by: TSSRALBI | last post by:
Hello I'm a network technician in training and I need your help. I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs. The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols. I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
0
4633
by: adsilva | last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
3
2012
bsmnconsultancy
by: bsmnconsultancy | last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.