Log exceptions on client and server under Node.js

Some users of JSNLog

You probably log server side exceptions and other events using a logging package such as Winston.
However, you're not logging client side events. This makes fixing bugs in live client side code much harder.
Fix this by installing JSNLog. It automatically logs client side exceptions to your server side log.
Log other JavaScript events as well, such as AJAX timeouts:
```
JL().error("..message..");
```
JSNLog sends the log data to the server and into your server side log.
Your logs now have both the server and client side events. You can correlate them with request ids.
Install JSNLog

Supports IE 8+, Firefox, Chrome, Opera, Safari (desktop/mobile).
Free, open source (MIT).
Use stand alone, as an AMD module or ES6 module or CommonJS module. Available on cdnjs.
No dependencies on other JavaScript libraries.
Fully documented: API docs, examples, how to's.

JL().info("log message");

JL("jsLogger").info("log message");

try {
  ...
} catch(e) {
  JL().fatalException("Exception info", e);
}

JL("jsLogger").setOptions({ "level": 4000 });

JL().setOptions(
{ "userAgentRegex": "MSIE 7|MSIE 8" });

var obj = {"f1": "v1", "f2": "v2"};
JL().log(2500, obj);

JL().log(2500, function() {
  // Only executed when log info will actually be logged.
  var loginfo = expensiveOperation();
  return loginfo;
});

Great if your site is used on mobile devices.

// Only log messages with severity ERROR or higher
JL().setOptions({ "level": JL.getErrorLevel() });

JL("jsLogger").setOptions(
{ "disallow": "suppress me" });

JL.setOptions({"maxMessages": 3});

appender.setOptions(
{ "batchSize": 3, "batchTimeout": 1000 });

To solve JavaScript exceptions, you often need to know what happened before they happened.
But you don't want to send trace messages with that context unless there actually is an exception.
Solution: JSNLog lets you buffer log messages on the client, and only send them when there is a fatal message.