This page is built with the CEN stack (Contentful, Eleventy & Netlify). For example you can arrange your data in a pretty fashion in the terminal and if isTTY is undefined you switch to a way that is easier to parse. For logging, we usually have requirements, which the console module can't do. Writing readable log lines are equally important for both humans and computers: you'd like to quickly understand what is going on, while machines have to parse the file as well. Sometimes multi-transport logging appears as a requirement - but it shouldn't be. To use the debug library, first install it: Let's try it by creating a new file that will simulate our library called random-id.js and place the following code in it: This creates a new debug logger with the namespace mylib:randomid and then logs two messages to it. The problem is that your library might want to log things for debugging purposes but really shouldn't clutter the application of the consumer. TTY stands for "teletypewriter" and in this case specifically for Terminal. For me, util.debuglog will be a good alternative for debug in smaller projects and scripts. To enable this logger, you have run your application with a special environment variable, called DEBUG. As such, the log file is already written to file and can be accessed by a number of tools or indeed anything that will read a text file. You can find me on Twitter, GitHub & YouTube. Re-run your server with a command like the following (assuming you installed pino-colada) : You'll now see your debug logs of the library in the same format as your application logs. debug for example colors your log messages nicely. Then, if every log line is labeled with this ID, you can search for these events. It allows us to write messages under a "namespace" and if the user of the library includes the namespace or a wildcard that matches it in their DEBUG environment variable, it will output these. Install both pino and express-pino-logger: Afterwards update your index.js file to use the logger and middleware: In this snippet we created a logger instance of pino and passed it into the express-pino-logger to create a new logger middleware to call app.use with. It's good to know about util.debuglog but as David points out, it doesn't cover all the functionality of debug. Typically these use cases fall into one of the following categories: We'll skip the first two in this blog post and will focus on the three Node.js based ones. You could even display them with emojis using pino-colada. There's lots of things going on under the hood of express and you might want to take a peek under the hood when you debug your application. The missing colors may not be a breaker for you but they are very welcome for lots of people debugging larger apps. By running LOG_LEVEL=debug node index.js we can adjust the log level. If you didn’t enable debug logging, you'll not see any of this. If you request http://localhost:3000 again you should also see your debug message. Install chalk using npm install chalk and create a file called cli.js. Start today with Twilio's APIs and services. In a nutshell, this allows us to use the redirect (>) and pipe (|) operators to work with error and diagnostic information separate from the actual outcome of an application. a timestamp. With the console module, you can put messages on both the stdout and stderr: This approach has a lot of flaws like you cannot turn it off or add log levels to it. The most basic kind of logging one can think of is using the built in console logging. Update your cli.js file to check for it: Now run node cli.js in your terminal and you see true printed followed by our colored message. Distributed tracing aims to eliminate this problem by providing insights on transactions and errors in a way that log files are not capable of doing so. Prefer RSS? Options are: 1. fatal- only those errors which make the application unusable should be recorded 2. error- record errors which are deemed fatal for a particular request 3. warn- record problems which are non fatal 4. info- record information about the general running of the application 5. debug- record information which is more verbose than info 6. trace- record very detailed logging 7. off- no log messages at all Other than off, each level includes messages at higher levels - for … To do so, I’ve compiled the tools, methods, rules and best practices we use at RisingStack for developing enterprise Node projects. When you run this code in your terminal, you won't see anything. Run in your terminal: All your logs will now be piped using the | operator into the pino-pretty command and your output should be cleaned up to contain crucial info and should be colored. This post is part of my Today I learned series in which I share all my learnings regarding web development. A few of those are: I personally like pino because it's fast and has a nice ecosystem. Navigate to http://localhost:3000 again and you see another line of JSON added. The aim of this article is to provide help with logging in Node.js modules, applications and distributed systems (or microservice architectures). Node.js will also start listening for debugging messages if it receives aSIGUSR1 signal. If you have questions or recommendations regarding this topic, feel free to share them in the comments section. This post is purely an introduction into the various ways and available logging solutions. Full-stack Development & Node.js Consulting. Now that we've learned a bit about the underlying tech aspect of logging, let's talk a bit about different use cases where you might want to log something. Information such as: Additionally, now that we know that everything goes to stdout and stderr anyways, we would probably want different log levels and the ability to configure and filter our logs by them. Additionally we replaced the console.log on server start-up with logger.info and added an additional logger.debug to our route to show different log-levels. Download, test drive, and tweak them yourself. The output from a sample express run looks something like this: When it comes to your application, you can do more sophisticated application logging. This includes making it human readable or uploading it to a cloud host. Running the script with an app-* environment variable leads to the following: The NODE_DEBUG environment variable can also be used to get debug messages from Node.js internals. The stdout stream is meant for your application’s output. When you run node index.js to execute your server and navigate to http://localhost:3000 you'll notice that it will print a lot of information that we don't really need. This way we can dynamically change what should be logged: When you are logging on a silly level, you should try to log almost everything. For example button presses or a redirected output (we'll get to that in a second). Let's use it in our index.js from the previous chapter: If you re-run the server but this time with DEBUG=mylib:randomid node index.js it prints the debug logs for our 'library". For example: process.stdout.isTTY. Place the following into it: Now if you would run this script using node cli.js you'll see colored output. The target should always be the standard output/error. This is done through a package fittingly called debug. In-depth articles on Node.js, Microservices, Kubernetes and DevOps. In this situation, you can use the debug module. One scenario is that your CLI might be used in the context of a Continuous Integration (CI) system and therefore you might want to drop the colors or any fancy decorative output. I would like to enable debugging using a parameter when starting up my application, for instance node myApp.js -d. Further my module should then only call the console.log if debugging is active. Log events can have different severity levels - in some cases, you just want to log events with at least a warning level, sometimes log lines have to be more verbose. If you know or find any tools that I should definitely mention or if you have any questions, feel free to drop me a line. For any logic logs, you should use a library like debug. For that, you have to use a so-called correlation identifier - and pass it to all the services the transaction goes through. How to create a diff of npm package releases on the command line, Prevent npm install for not supported Node.js versions, The fs module includes promisified methods since Node 11. Once a month I share articles, GitHub projects, lots of learnings, talks, some #devsheets and some music. However, in some cases, application developers may need it to understand better why a given issue arose. Currently I'm having a lot of console.log in my modules. (SIGUSR1is not available on Windows.) Whether talking about Node.js modules or complete applications, it is crucial to get logging right. If you restart your server by running again node index.js, you see a quite different output that prints a JSON for every line. Many of them are debug-messages, which I only need to see, if I'm debugging my application. While millions of packages depend on the very popular debug package, it turns out that Node has similar functionality built-in via util.debuglog. Your library should be silent by default and leave writing output to the user. You will need a timestamp for that. When you write the following code in Node.js in a file called index.js: And execute it in the terminal using node index.js you'll see the output of the two directly under each other: However, while those two might look the same, they are actually treated by the system differently. Place the following into the index.js file: We are using console.log('%O', req) here to log the entire object. Every process has three default streams that it can work with. Today I saw a quick conversation on Twitter between @ThisIsMisEm and @davidmarkclem, which unveiled an interesting fact about Node.js.