How to log exceptions in JavaScript

user_113141 0
Viewed 78649

As a C# developer I'm used to the following style of exception handling:

try
{
    throw SomeException("hahahaha!");
}
catch (Exception ex)
{
    Log(ex.ToString());
}

Output
------

SomeNamespace.SomeException: hahahaha!
    at ConsoleApplication1.Main() in ConsoleApplication1\Program.cs:line 27

Its really simple, and yet tells me everything I need to know about what the exception was and where it was.

How do I achieve the equivalent thing in JavaScript where the exception object itself might just be a string. I really want to be able to know the exact line of code where the exception happened, however the following code doesn't log anything useful at all:

try
{
    var WshShell = new ActiveXObject("WScript.Shell");
    return WshShell.RegRead("HKEY_LOCAL_MACHINE\\Some\\Invalid\\Location");
}
catch (ex)
{
    Log("Caught exception: " + ex);
}

Output
------

Caught exception: [object Error]

EDIT (again): Just to clarify, this is for internal application that makes heavy use of JavaScript. I'm after a way of extracting useful information from JavaScript errors that may be caught in the production system - I already have a logging mechanism, just want a way of getting a sensible string to log.

exception-handling javascript
9 Answers

You can use almost in the same manner ie.

try
{
    throw new Error("hahahaha!");
}
catch (e)
{
    alert(e.message)
}

But if you want to get line number and filename where error is thrown i suppose there is no crossbrowser solution. Message and name are the only standart properties of Error object. In mozilla you have also lineNumber and fileName properties.

user_944280

I'm not sure whether or not it is cross browser or if it's what you are looking for, but I suggest you try:

window.onerror = function (err, file, line) {
    logError('The following error occurred: ' + 
    err + '\nIn file: ' + file + '\nOn line: ' + line);
    return true;
}
user_1340980

I had a similar problem.

Using console.table(error); worked well for me. It displays information in a table, and also lets me expand/collapse to see more details.

user_61275800
Dorward_190680
user_836640

I wrote a handy function for it


const logError = (e: any) => {
   if (console.error) console.error(e, e.stack);
   else console.log(e)
}
user_135878860

The modern best practice (as I understand it) is to log the error as a separate argument to console.error (or console.log, console.warn, etc...)

try {
  maybeThrows()
} catch (e) {
  console.error('it threw', e);
}

Trying out this approach in practice:

try {
  throw Error('err') // Error object
} catch (e) {
  console.error('it threw', e); // it threw Error: err
}

try {
  throw 'up' // not an error object
} catch (e) {
  console.error('it threw', e); // it threw up
}

I ran the above in Chrome, and Node v16. Note that node did not include a stack trace for throw 'up', but did for the proper error. Chrome included the stack for both.

user_3637010
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