I've built a custom logging utility which displays a Log Message and the DateTime. I would like to add the line number in the source code which called the function.
Is there a way to determine which line of the HTML source a particular javascript function was fired?
Having written a logging library (log4javascript) myself, I've considered this same problem and here are my thoughts:
The problem is that in order to get the information you want, you need an Error object that was created on the line in question. Creating an Error within your logging utility will only directly give you the filename and line number for the particular line in your logging utility code rather than for the line of code that made the logging call. The only way round this I can think of is parsing the stack property of the Error (or the message property in Opera), which has several problems:
the stack trace is only available in Mozilla, recent WebKit and Opera browsers
the stack trace is a string that varies from browser to browser, and may change format again without notice in future browsers, thus breaking the parsing code
throwing an Error and parsing its stack trace for every log call will add a significant performance overhead.
For the purposes of log4javascript, I decided it wasn't worth implementing, but for your own needs you may decide it's worthwhile.
Related
I'm learning v8 now, but I have encountered some problems.
How to set a breakpoint a method's start address in memory if I want to debug a method's C++ implementation.
e.g. var a= new Array(0,1); a.indexOf(1) ; I want to set a breakpoint at slice's beginning, or are there other ways to track the assembler code ?
There are a lot of functions will be complied and writed into a file named snapshot.bin. so I can't set a breakpoint at the beginning of these functions.
You need to check the source code and find the implementation of slice. Then set a gdb/lldb break point in that .cc file: byiltins-typedarray.cc
A lot of functions are defined as builtin or runtime functions.
It depends on the kind of function you want to inspect.
You can compile without snapshot to get around snapshot-related debugging difficulties (at the cost of making startup quite a bit slower: several seconds in Debug mode).
You can modify the respective code generator to emit a break instruction at the beginning of the function. For the example of Array.indexOf, that's probably the easiest solution; the CodeStubAssembler instruction is called DebugBreak().
You can break somewhere else using GDB, find your way to the function in question (e.g. via isolate->builtins), and set a breakpoint on the address of its entry. (This requires a bit of V8 knowledge and/or code reading skills, but it's not difficult.)
You can use various --print-*-code flags to print code to stdout (without breaking on it).
I am finding it difficult to locate where an error occurs in javascript on a client I have no access to. Currently I trap the error with onerror and send the arguments to a log on the server.
Unfortunately the line number is no help because numerous javascript files get included, causing the line number to not correspond to anything I have access to.
So if I get something like "n is not defined", and n occurs many times in the function, I have no way to locate where it happened.
I have been trying to reference the code on the line throwing the error say "x=n * 5 + 4", then I could search for that code, but have had no luck referencing the actual code on a line from within javascript.
So how does one locate the line that threw the error in this situation?
client uses firefox only, if that matters.
I have no access to client
This is not one error I am stuck on, but working on how to track an error in this situation
Your best bet would be to use Firefox's debugger.
Open dev tools
Go to the debugger, select the .js file you want, and hit the little {} button in the bottom left (depending on version yours may be in a different location) -- this will prettify the JavaScript
Set breakpoints by clicking next to line numbers
From here on out you have to do this old-fashioned. Cast a breakpoint net around your trouble code, then keep narrowing down the lines until you find the occurrence that causes the error.
Of course, once you find the line it still won't be 1-to-1 with the original code, but hopefully the breakpoint exercise will at least reduce the scope of code/logic you have to dig through.
use your debugger to enable breaking on error. once you break, look at your locals for clues about your location. go up the stack and look at each frame.
you should be able to trace n up the stack and find out why it was null
the little {} that william suggested is also helpful
I've set up a simple testbed for WatiN (ver 2.1) which reads:
var browser = new IE();
browser.GoTo("http://www.google.co.il"); // webpage doesn't matter really
browser.RunScript("alert(123)");
This works only if KB3025390 is not installed. Installing it breaks the above test with an UnAuthorizedAccessException which has HRESULT set to E_ACCESSDENIED. What gives? Is there any workaround?
Update: Using IWebBrowser2.Navigate2 along with "javascript:console.log(123)" type of scripts works however
it makes me feel uneasy using such a backchannel
the scripts run through this back-channel of .Navigate2() may only have a max length of about 2070 chars (give or take) otherwise they get forcibly truncated to this length leading to javascript errors upon attempting to run them
using .Navigate2(), even with the most trivial script, will clog the ready state of Internet Explorer for good in the sense that it will be set to READYSTATE_LOADING without any hope of getting rid of it. In simple terms this means that once you use this hack, you either have to perform every single subsequent operation in WatiN in a "dont-wait-for-webpage-to-load" fashion (GoToNoWait, ClickNoWait etc) lest your code freezes upon waiting for the browser to turn back to READYSTATE_COMPLETE (which will never come about ofcourse as already mentioned).
there appears to be a much broader issue here in the sense that I can't even access the properties of an IHtmlWindow2 object p.e. window.document throws an unauthorized exception again making it virtually impossible to transfer over to the C# world the return-values of the scripts I'm running (using Expando etc) for documents other than window.top.document (for the window.top.document window there is IWebBrowser2.Document which does the trick)
Update#2: The folks over at the selenium project have also noticed this issue:
https://code.google.com/p/selenium/issues/detail?id=8302
A bug report has been created as well:
https://connect.microsoft.com/IE/feedback/details/1062093/installation-of-kb3025390-breaks-out-of-process-javascript-execution-in-ie11
Update#3: IHTMLWindow2.setInterval and IHTMLWindow2.setTimeout also throw UnauthorizedAccess exceptions. These methods are not marked as deprecated in:
http://msdn.microsoft.com/ko-kr/library/windows/desktop/aa741505%28v=vs.85%29.aspx
yet they have wounded up suffering from the same cutbacks all the same.
Update#4: I gave the approach recommended in this post a shot:
https://stackoverflow.com/a/18546866/863651
In order to dynamically invoke the "eval" method of the IHTMLWindow2 object (or any other method really). Got the same "System.UnauthorizedAccessException" as above. So no joy here either.
Microsoft recommends using "eval" over "execscript" however after the above experiment I suspect that they are refering to accessing "eval" only from within the browser.
As far as I can tell thus far, when it comes to the full-fledged IE11+ using "eval" out-of-process (via COM) appears to have been completely prohibited along with any other function-invocation of the window object, the only exception being the back-channel of the .Navigate2() mentioned above.
It turns out Microsoft eventually backpedaled on its decision to kill off .execScript at COM-level. Just install the latest updates for Windows including kb3025390: One of the updates for IE that came after kb3025390 brings back .execScript functionality at COM-level
Note, however, that .execScript is not accessible through IE's javascript anymore. In that context it's gone for good.
fyi: this one is also not working
ieInstance.Document.Script.<methodNameString>(<commaSeperatedParameterString>)
try this worked for me at some places but not all places
ieObject.Navigate "javascript:<methodNameString>(<commaSeperatedParameterString>)", Null, "_parent"
or
ieObject.Navigate2 "javascript:"<methodNameString>(<commaSeperatedParameterString>)", Null, "_parent"
now trying to find out solution using eval
I have found a way around the problem of an update installing automatically. You can just create a simple batch file with following content.
{code}
#echo off
wusa /uninstall /kb:3025390/quiet /norestart
END
{code}
Then go to task scheduler, create a new task for this batch file to run every one hour or day as per your requirements. Add it as a system task so it runs in the background and does not affect the running automations.
I am working in FireFox and I notice that a exception is thrown in my Firebug console.
The exception is in a jQuery function, but I have no idea who the caller is.
The webpage has a lot of custom javascript files included with many lines of code.
Is there any trick that I can use to find out from where the call came?
I have tried removing some of the included javascript files, but due to the size of the project and how things are connected, it is limited.
I tried placing a "debugger;" attribute in a javascript file and just stepped through the code, but it doesn't seem that I hit the correct place doing this.
One way to find the caller is to put a breakpoint in the jquery line where the exception is thrown. Then you will be able to go through the call stack and see how is the first caller.
But be carefull with firebug, sometime when you put breakpoints, you get a different behaviour if you have multiple asynchronous call. If this is your case, use Chrome debugger to manage this.
Often the error in the console does not include a trace or error object, but just a simple message like :
object is undefined
length = object.length,
so I can't easily find the part of the app that is calling jquery with the faulty data.
At present I am tracking them down by entering a long trail of logs until I find the broken code. This is time consuming and is becoming more so as the app grows in complexity. Is there an easier way?
Edit: to add screenshot
In the console where you see the error:
click the circled part so that it becomes fully red:
then refresh the page. Firebug will break at the error, interrupting the execution of the script at that precise point.
You can now examine the stack trace (which includes the call stack), and use "Watch" to watch the value of variables.
in firebug you can write conlose.log(object name) then open the console you will get complete object.
Use debugger (inside the function calls where u expect to receive values from controller)inside the script.