Getting ready

Starting with version 1.0, Socket.IO doesn't show any logging by default. However, it can easily be turned on. Behind the scenes, it will use an NPM module called debug, which allows logging to navigate to various scopes that can be turned on or off as needed.

How to do it…

To enable debugging on the client side, follow these steps:

How it works…

The localStorage object in the browser is an object with key/value pairs that is maintained when you refresh the page or leave it entirely. It is useful for persisting data on the client side in modern browsers.

Socket.IO uses the debug NPM module. This views the localStorage key to determine the logging level to be displayed in the browser. The fact that the debugging level is set in localStorage can be very useful because you can set a debugging type anywhere even in production, and it will only log on to your machine. Also, you will be able to refresh the page and see the Socket.IO logging from the initial page load, which can be really handy for debugging events that occur earlier on the page life cycle.

There's more…

Not only can you set the logging to show everything, you can also listen for only certain log types by setting them up in localStorage. For example, if you are only interested in XHR requests, you can ask to only see messages in the engine.io-client:polling-xhr namespace with the following code:

localStorage.debug = 'engine.io-client:polling-xhr';

You can also set multiple log types by separating them with a comma, as shown in the following code:

localStorage.debug = 'engine.io-client:polling, engine.io-client:socket';

See also

The following recipe, Debugging on the server.