Generate heap dumps and detailed output for uncaught exceptions and critical errors


Exception is nifty little module that will make your life a lot easier when your applications start crashing. So what makes Exception exceptional:

  • git: When it detects that your application runs from git repository it will automatically include the sha1, branch and even it's configuration in the output.

  • process: Useful information like load average, uptime, free memory, heap size, process id and even the build information of your node process are included.

  • modules: A dump of all loaded modules is included. This includes node's modules, native compiled modules and user modules.

  • heapdump: We automatically generate a heap dump of your process. This allows you to inspect the state of the application during the crash.

And much much more. If you need more information do not hesitate to create an issue on our Github issue tracker because that same information might also be useful for others!

To store all this information in a redundant way we support different modes of outputting this data:

  • disk: We automatically create an exception folder your current working directory where all dumps will be added. With the disk mode we add a JSON document of all the information as well as the .heapsnapshot of the process.
  • console: We output the information to stderr.
  • remote: Alternatively you can store this information in a database.

See the usage section for detailed information.

This module is released in npm and we advise you to only include this module once in your application. This module is not meant as library dependency but as application dependency. So to install this module as dependency of your application run:

npm install --save exception

If you're stubborn and want it as library dependency run:


In all the examples we assume that you've required the library in your application using:

'use strict';
var Exception = require('exception');

To temporary disable exceptions being processed by this module set an enviroment variable.

EXCEPTION=false npm run something

This requires the Exception class so you can generate new exceptions. One of the places where you want to generate an exception is in the uncaughtException handler. You can do this manually using:

process.once('uncaughtException', function derp(err) {
  var exception = new Exception(err);

Or use our convenience method:

The exposed .listen function will automatically assign a process.once(uncaughtException) handler which will automatically save the exception for you and a process.on(SIGUSR1) which will generate heap dumps every single time it's called.

You can supply the .listen function with a callback which will be called once the exception has been saved so you can exit the process your self. If you do not exit the node process we will attempt to abort the node process so the operation system will also generate a dump of the application.

// or 
Exception.listen(function fn() {

As you've might have read in the intro, we support different ways of storing data. One of these ways was remote storage. In order to use this you need to create a custom instance of Exception and extend it with a custom remote method:

var CustomException = Exception.extend({
  remote: function remote(fn) {
    putthisshitinmongodbmethod(this.JSON(), fn);

We assume that the putthisshitinmongodbmethod does your fancy pancy database / storage call and calls the fn when completed.

By default we just dump all the information in the process.cwd() of your node process. This can be less then ideal in certain cases as you might want to store the heapdumps and json dumps on a different disk. You can configure the location of the dumps by changing the directory property:

var CustomException = Exception.extend({
  // imagine that this comment is actually the remote code of the example above. 
  directory: '/my/root/volume/shared/goat/waffles'

You can now use your custom exception in the exact same way as the regular exception:

process.once('uncaughtException', function (err) {
  var exception = new CustomException(err);
// and even the .listen method would still work: 

In the example code above you might have noticed the .toJSON method. We got a bunch of those available. Here's a list of all of the things that is available:

Generate the JSON dump and return it. As this method is called toJSON it will also automatically be called when you run JSON.stringify(exception).

var exception = new Exception(err);
var data = exception.toJSON();

Generate a some what human readable output. (Just a prettified JSON output atm, pull requests regarding this will be accepted in a heartbeat. Was intended for development purposes).

var exception = new Exception(err);

Write the exception's JSON dump to disk and generate the heapdump. Please note that this is a synchronous process and that your node process will stall for a bit. But this is worth it in the end as you wouldn't be generating exceptions if something is seriously fucked up.

var exception = new Exception(err);

Write the JSON dump to the console. With an empty line before and after the dump. It uses console.error which will write the output to stderr and console.* is blocking write call to stderr.

var exception = new Exception(err);

This function does nothing by default. It's just a process.nextTick which calls the supplied callback. It does nothing because it's left for you to implement it. See extending exceptions.

This saves the exception using the console, disk and remote method. Redundancy all the exception outputs. When no callback is supplied in this method we will automatically attempt to destroy your node process using process.abort() so the OS can save a core file of the app. This should be the recommended approach for storing your exceptions.

var exception = new Exception(err);

Of course, actions speak louder than words, but I hope that it's same with example output:

  "node": {
    "http_parser": "1.0",
    "node": "0.10.28",
    "v8": "",
    "ares": "1.9.0-DEV",
    "uv": "0.10.27",
    "zlib": "1.2.3",
    "modules": "11",
    "openssl": "1.0.1g"
  "version": "0",
  "environment": {
    "args": [
    "node": "/usr/bin/node",
    "cwd": "/Foo/Bar/Directory/exception",
    "env": {
      "Apple_PubSub_Socket_Render": "/tmp/launch-KN4Qeq/Render",
      "LANG": "en_US.UTF-8",
      "TERM": "xterm",
      "USER": "V1",
      "DISPLAY": "/tmp/launch-rebH0I/org.macosforge.xquartz:0",
      "TERM_PROGRAM": "iTerm.app",
      "ITERM_PROFILE": "Molokai",
      "__CHECKFIX1436934": "1",
      "SHELL": "/bin/zsh",
      "SHLVL": "1",
      "ZSH_THEME": "3rdEden",
      "HISTFILE": "~/.zsh_history",
      "HISTFILESIZE": "65536",
      "HISTSIZE": "10000",
      "SAVEHIST": "10000",
      "EDITOR": "vim",
      "GREP_COLOR": "1;32",
      "PAGER": "less",
      "LESS": "-R",
      "LC_CTYPE": "en_US.UTF-8"
    "gid": 20,
    "uid": 501
  "git": {
    "checkout": "refs/heads/master",
    "sha1": "d6c64e37370b4205000a6f67bc358a8d2dacd5af"
  "system": {
    "platform": "darwin",
    "arch": "x64",
    "hostname": "Fortress-Maximus.local"
  "process": {
    "load": [
    "uptime": 2454790,
    "freemem": 2333417472,
    "totalmem": 8589934592,
    "heap": {
      "rss": 13701120,
      "heapTotal": 6163968,
      "heapUsed": 2073320
    "pid": 10011,
    "features": {
      "debug": false,
      "uv": true,
      "ipv6": true,
      "tls_npn": true,
      "tls_sni": true,
      "tls": true
    "modulesloaded": [
      "Binding evals",
      "Binding natives",
      "NativeModule events",
      "NativeModule buffer",
      "Binding buffer",
      "NativeModule assert",
      "NativeModule util",
      "NativeModule path",
      "NativeModule module",
      "NativeModule fs",
      "Binding fs",
      "Binding constants",
      "NativeModule stream",
      "NativeModule _stream_readable",
      "NativeModule _stream_writable",
      "NativeModule _stream_duplex",
      "NativeModule _stream_transform",
      "NativeModule _stream_passthrough",
      "NativeModule os",
      "Binding os",
      "UserModule .",
      "UserModule heapdump/build/Release/heapdump",
      "UserModule fusing",
      "UserModule predefine",
      "UserModule extendable",
      "UserModule ./package",
      "UserModule moduleloadlist"
  "exception": {
    "ocurred": "2014-08-18T18:53:21.136Z",
    "ms": 1408388001136,
    "message": "fucked",
    "stacktrace": [
      "Error: fucked",
      "at Object.<anonymous> (/Foo/Bar/Directory/exception/example.js:11:7)",
      "at Module._compile (module.js:456:26)",
      "at Object.Module._extensions..js (module.js:474:10)",
      "at Module.load (module.js:356:32)",
      "at Function.Module._load (module.js:312:12)",
      "at Function.Module.runMain (module.js:497:10)",
      "at startup (node.js:119:16)",
      "at node.js:906:3"