We Keep Coding

Javascript URL Navigation Handling Interfering with other Javascript Sections

Two aspects of my project's Javascript are interfering with each other. Not sure why, or how to resolve.
I have the following in my code, in order to allow for a URL hashtag action:
function getHashValue(key) {
return location.hash.match(new RegExp(key+'=([^&]*)'))[1];
}
var hash = getHashValue('hash');
console.log(hash);
I'm also running video.js and bigvideo.js within my Rails project. For some reason, the javascript code above prevents the other javascript (my bigvideo implementation) from functioning. Why? How do I resolve?
My bigvideo implementation is described here: https://stackoverflow.com/a/17581187/1318135

It seems possible that getHashValue is throwing an exception (array limit exceeded?) which could interfere prevent other code on the thread from running. Try enclosing the return statement in a try/catch.

Here's what you get: TypeError (exception) Cannot read property '1' of null.
Catch the exception and you'll be okay, I think.

Programatically retrieve count of javascript errors on page

I'd like to write a test case (using Selenium, but not the point of this question) to validate that my web application has no script errors\warnings or unhanded exceptions at certain points in time (like after initializing a major library).
This information can easily be seen in the debug consoles of most browsers. Is it possible to execute a javascript statement to get this information programatically?
It's okay if it's different for each browser, I can deal with that.

not so far read about your issue (as far as I understood your problem) here
The idea be the following:
I found, however, that I was often getting JavaScript errors when the page first loaded (because I was working on the JS and was introducing errors), so I was looking for a quick way to add an assert to my test to check whether any JS errors occurred. After some Googling I came to the conclusion that there is nothing built into Selenium to support this, but there are a number of hacks that can be used to accomplish it. I'm going to describe one of them here. Let me state again, for the record, that this is pretty hacky. I'd love to hear from others who may have better solutions.
I simply add a script to my page that will catch any JS errors by intercepting the window.onerror event:
<script type="text/javascript">
window.onerror=function(msg){
$("body").attr("JSError",msg);
}
</script>
This will cause an attribute called JSError with a value corresponding to the JavaScript error message to be added to the body tag of my document if a JavaScript error occurs. Note that I'm using jQuery to do this, so this specific example won't work if jQuery fails to load. Then, in my Selenium test, I just use the command assertElementNotPresent with a target of //body[#JSError]. Now, if any JavaScript errors occur on the page my test will fail and I'll know I have to address them first. If, for some strange reason, I want to check for a particular JavaScript error, I could use the assertElementPresent command with a target of //body[#JSError='the error message'].
Hope this fresh idea helps you :)

try {
//code
} catch(exception) {
//send ajax request: exception.message, exception.stack, etc.
}
More info - MDN Documentation

Error: can not cal method 'addCls' of null {ExtJs4}

I'm using Bryntum chartsand extjs4 for my project.
This is the error I am getting since yesterday
I understand that the method addCls is not defined.
How to tackle this error.
My code file is very big somewhere around 1500 lines, But if it is required for the understanding of question then i will paste the whole code too....
Any help will be appreciated.

put a breakpoint on the line that throws an exception. Figure out which object (culprit) is trying to call addCls() method and then edit the breakpoint to add a condition like this:
culprit == undefined
next time code will halt just before you hit your bug. you can then inspect the stack and see the call hierarchy to this point.

JavaScript - is it possible to force code execution after an error?

I'm trying to make a PoC of reflected Cross-Site Scripting on a website that I'm testing right now. I've found a place inside of a Javascript code where commands can be injected, however the trouble is that there the previous block of code throws a 'not defined' error and therefore (at least I think so) my injected code is not executed. Is there any chance to execute the code anyway?
Here is the code:
UndefinedObject.Init({
Var1:"a",
Var2:"b",
Var3:"can_be_injected_with_JS_code")}
I can't inject any HTML tags as these are filtered by the application.
Many thanks!

Wrap them under try catch block.

In a sequence of execution, if the code fails, the remaining part will not be executed. Javascript errors ("Exceptions") can be caught using try...catch (if you are able to inject this try - catch also).
If there is a different flow (via another event), the code will continue.

You can either try using a try-catch, or if that won't help, try using window.onerror

Generally the right way of doing that is using try-catch-finally or try-finally:
If you make something about the error - log or do something else. Catch may be also used to execute your code, but not a good practice. You can do nothing about the error if you want, that`s why finally is used.
Finally is used when it is important to execute a piece of code, no matter if an error is thrown or not. For example in C++ or other language when you work with files inside finally the file is closed ( you can not leave it opened ). Look here for some examples.

on a javascript error, how to identify method or js file with the problem?

When a javascript error occures in IE (or in other browsers) you get a popup saying that javascript error has occurred - usually this comes with a line number and some hint.
Sometimes it comes with line 0 and with no way of knowing what the problem is.
Javscript can come from HTML itself, from a js file or from JSP (and more).
Microsoft has a script debugger that helps a lot in finding where js errors are, however sometimes when a js error occurs the script debugger cannot find the code portion and thus its difficult of finding where is the root cause of the problem.
My question is whether anyone knows any way of making script debugger find the code any way (mostly happen with js code that is in JSP file), or at least include in the IE popup the method or js file where the error has occurred. (it only display the line number, and many times its line 0...).
Thanks,
Tal.

The error object which is created when an error is thrown by JavaScript is very unreliable when it comes to the source line, especially within IE. Browsers like Firefox and Safari are better at line numbers, but they are generally pointless due to minification of the files.
What is obviously of more use is getting the call stack, but due to the anonymous nature of JavaScript functions (well, that they can be anonymous) a call stack can often be hard to work out.
If you're doing a try/ catch you can do arguments.callee which will return you the method which called the current method which failed.
Here's a good example of doing a complete stack in JavaScript - http://eriwen.com/javascript/js-stack-trace/

Also developer tools included with Internet Explorer 8 is something good to trace and debug your javascript code

There is a version of Firebug called Firebug Lite that will work with Internet Explorer. It's performance is going to be based on how complex your pages are; however, for relatively lightweight pages, it should provide some insight.
I recommend this tool rather than simply using Firebug and Firefox because not all errors that occur in Internet Explorer will occur in Firefox, and so performing any debugging in that browser may not yield any results.

Firebug on Firefox is usually considered one of the best debugging tools.
On Firefox, go to
http://getfirebug.com
to get it.

This will print you a stack trace:
function Stack()
{
try
{
throw Error()
}
catch(ex)
{
return ex.stack
}
};
print( Stack() );

If all else fails (and when dealing with IE it sometimes does) you can always walk through your code with alerts. It's crude and tedious, but sometimes it's all you can do:
Simply:
var count = 0;
then sprinkle some:
alert(count++);
at strategic lines along your code and note where it stops alerting.
Lather rinse repeat until you have your line.

If using Firefox you can press Ctrl + Shift + J to bring up the JavaScript error console that is built into Firefox, which will tell you exactly what went wrong.