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
Related
I made a function called test() in javascript file.Placed a simple alert into it.
In html file, called the method on click of a button. But,it was not being invoked.
Problem was in the 11th function, nowhere related to mine !!!! But, how can a person making his first javascript function suppose to find that out ???
I am looking for best ways to debug javascript.
You can debug javascript using many modern browsers. See this question for details on how to debug in Google Chrome:
How do you launch the JavaScript debugger in Google Chrome?
Furthermore, you shouldn't use alert() for debugging as this can give different results to a production version due to alert() causing a pause in the script.
It is best practice to use console.log() and view the output in the browsers Console.
You can also put debugger in your javascript code to force a breakpoint. However I prefer not to use this as forgetting to remove this before deployment will cause your script to pause, which can be quite embarrassing!
You should use the debug console provided by the browser.
Chrome has it inbuilt, press CTRL + SHIFT + j. In Firefox, install Firebug plugin.
In your code, add alert() to show flow and get values of variables.
Also, use console.log() which will only output to the debug console.
Depending on your browser choice there are debugging options - I tend to use Firefox, so Firebug in my case. There is a question that list options for other browsers - What is console.log and how do I use it?
Unless the project you're working on has already adopted a mechanism for debugging, console.log() tends to be a simple and useful option when tracking down a problem.
Whilst debugging you could take the approach to log out a line when entering a function, like so:
var myFunc = function(el) {
console.log('Inside myFunc');
// Existing code
};
This will enable you to see which functions have been called and give you a rough idea of the order of execution.
You can also use console.log() to show the contents of variables - console.log(el);
Be mindful to remove/disable console.log() calls once you're done as it will likely cause some issues in production.
To answer your question within question,
how can a person making his first javascript function suppose to find that out ???
Well, when something is wrong in JavaScript, for example, you made a syntax error - the script will stop working from there. However, this won't stop HTML from rendering on, so it might look as if everything is correct (especially if your JS is not changing the look of the page) but all the functionality of JS will be dead.
That's why we use the debug tools (listed in the other answers here) to see what's wrong, and in cases like this, it's very easy to notice which function has errors and is causing the whole script to break. This would probably have save a few minutes to your seniors as well.
The best approach would be to test frequently so that whenever you run into errors, you can fix them right away.
I am a chronic user of Firebug, and I frequently need to log various stuff so that I can see what I am doing. The console.log function is a lot to type. Even if I assign it to a single letter variable like q = console.log, I have to do it every time I fire up Firebug. Is there any way to do it such that q always refer to console.log (unless, of course, I override it in my session)?
To answer your question, the functionality doesn't currently exist, however I have found the firebug developers to be very responsive in the past. Why don't you put in a feature request on their forum, or better yet, code it up yourself, and ask them to add it?
Depending on your IDE, simply setup a code snippet (I use Flash Develop, so Tools -> Code Snippets).
I believe this to be a better way than setting up redirect scripts and what not, because it stops the Firebug namespace from being polluted, and makes it easier/more consistent to debug if your debugging breaks down.
The screenshot shows me using Flash Develop, hitting Ctrl+B, then hit enter. The pipe (|) in the snippet indicates where the cursor will be placed to start typing after inserting the snippet.
Our product inserts a script into client's websites, kind of like a live chat box.
Often, clients' websites have buggy javascript that also stops our code (the browser stops execution when errors are encountered). Is there any way to make our code still execute even though there are errors in the console about things like undefined methods or variables?
Thanks for your help.
The short answer is that you really can't.
"Solution" #1: You could insist that YOUR 3rd party code run before anyone else's. In most cases, this isn't possible or even desirable.
"Solution" #2: You could insist that the 1st party engineers wrap all 3rd party code in try/catch blocks. But, this solution really doesn't buy you any guarantee, because very frequently 3rd party libraries attach additional <script> tags to the page - these would not fall under the "jurisdiction" of the try/catch scope enclosing the code which created this/these tag(s).
"Solution" #3: You could build YOUR app entirely within the scope of an <iframe>, thereby avoiding the issue entirely. Unfortunately, even if you're very smart, you'll quickly run into cross domain violations, 3rd party cookie restrictions, and the like. It's very probable that this will not work for you.
"Solution" #4: You could explain the issue to your client, and have them demand that the other 3rd party code run cleanly. I say this is a "solution" because, frankly, it's not a "solution" to your question if your question is how to avoid doing exactly this.
Unfortunately, option #4 is your best bet. It may help if you observe other 3rd party libraries "breaking" in the same fashion: you can tell your client "hey, it's not just me - X, Y, and Z are all also 'broken' because of <name of other 3rd party library>." It may cause them to put the heat on the offending code, which makes the web a happier place for all involved.
As others have said, continuing after an error might not be the best thing to do but you can try this:
function ignoreerror()
{
return true
}
window.onerror=ignoreerror();
More details here
The onerror event fires whenever an JavaScript error occurs (depending
on your browser configuration, you may see an error dialog pop up).
The onerror event is attached to the window object, a rather unusual
place to take refuge in, but for good reason. It is attached this way
so it can monitor all JavaScript errors on a page, even those in the
section of the page.
Opera has a page with more details
Browsers supporting window.onerror
Chrome 13+
Firefox 6.0+
Internet Explorer 5.5+
Opera 11.60+
Safari 5.1+
You can't from your code - they need to use try/catch for questionable pieces of script.
You could have them insert an iframe into their page instead of you trying to inject code using a script tag like so: http://jsfiddle.net/EzMGD/ Notice how the script throws an error yet we can still see the content in the iframe. The iframe should help from using each others variables if applicable.
<script>
MeaningOfLife();
</script>
<iframe src="http://bing.com"></iframe>
Or inject the code so it's the very first or very last script.
Well, to me that work fine:
element = document.querySelector('.that-pretty-element');
if (element != null) {
element.onclick = function () {
alert(" I'm working beibi ;) ");
}
}
querySelector() returns false, so, we can verify with if's
I don't know if this has been asked before, but what i'd like to be able to do is get data from the error console within the browser itself(if it supports it) this would be for when a user sends off a bug report it'd pull up any errors related to pages at my website for things such as typos in code and other things that somehow managed to slip by. Also, in that regard is there a way to pass the errors from the console to a useable format? If this isn't possible, then i could just tell them to copy and paste what came up from the site itself.
I thought of this right now as i was thinking about how to make the bug reporting system run better since the entire thing is basically ran within the browser and for the backend I can easily just look at error logs but for the frontend ie javascript bits of things it's not goign to be as easy.
So to finish wrap all of this up in one little statement, is there an easy way to get the data from the error console and be able to send it along via javascript ie to a form, or something similar.
You can use the onerror event in JS to get the details of the error. Hoptoad do this for example and log the errors to their console, Their code re-uses lots of nice JS scripts including a printStackTrace function that is great.....
You can see how they do it here:
http://hoptoadapp.com/javascripts/notifier.js
I get the following error in firebug in Firefox 3 with both MooTools and jQuery:
"p.onStatusChange is not a function".
I've noticed this error frequently in firebug since one of the latest updates of FF3. However, it has started appearing with code that hasn't been changed in some time and that was not reporting errors previously. The errors happens when ajax results are returned. It shows up in different applications that use separate javascript libraries, MooTools and jQuery.
Does anyone have any idea why these errors are appearing? My intuition tells me that it is something in Firefox that changed, but I can't find any information online currently. The ajax calls still work fine, but I am wary of just going with my intuition and leaving script errors in my code.
Thanks,
Jason
I get it in tabBrowser instead:
chrome://browser/content/tabbrowser.xml
(4) errors occur:
p.onStatusChange
p.onProgressChange
p.onStateChange
p.onSecurityChange
What I found was that the add-on "PDF Download" was causing these errors. The best way for me to check was to go to a page that produced the errors, turn off all the add-ons, and turn them on one-by-one (starting with Firebug). Instead of going one-by-one, I actually turned them on in lots of 3 to help identify the problem sooner.
Here is the reference for the function NsIDownloadProgressListener. It looks like it has been deprecated.