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A Guide to Node.js Logging

difference between console.log and console.error in nodejs?
process streams stdin, stdout, stderr

通俗的理解就是标准输入，标准输出，标准错误输出其实是不同的文件描述符，最后会放到不同的地方

DEMO

index.js如下

console.log('Hello there');console.error('Bye bye');

node index.js > hello.log 2> error.log

When Do You Want to Log?

We are using console.log(’%O’, req) here to log the entire object. console.log uses util.format under the hood that supports additionally to %O other placeholders.

there’s often additional information we need

• Timestamp - to know when things happened
• Computer/Server Name - in case you are running a distributed system
• Process ID - in case you are running multiple Node processes using something like pm2
  -Message - an actual message with some content
• Stack Trace - in case we are logging an error
  Maybe some additional variables/info

Your Library Logs

如何开启其他库的日志

DEBUG=express:* node index.js

那么这个功能是怎么实现的呢？
This is done through a package fittingly called debug. 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.

npm install debug

Your CLI Output

https://www.twilio.com/blog/how-to-build-a-cli-with-node-js

In Summary

我们学习日志的过程
第一步，使用console.log()
第二部，我们想着去优化日志问题。
推荐的方法是看看那些开源的node项目是怎么解决日志问题的