Node. Js: Winston: Can I Add Default Meta Data to All Log Messages
I'm Using Winston in Node. Js for Logging. I Know I Can Add Metadata Individually to Each Log Message but Is There a Way to Specify a Default Set of Metadata...
I'm using Winston in Node.js for logging. I know I can add metadata individually to each log message but is there a way to specify a default set of metadata that'll be added to every log message (such as the app name) as I don't want to specify it every time I need to send a log message.
7 Answers
For Winston v2 (see comments)
There are now rewriters.
For example, the below will add a property app to every metadata going through this logger.
logger.rewriters.push(function(level, msg, meta) {
meta.app = 'myApp';
return meta;
});
You can also declare it when building the logger:
new (winston.Logger)({
level: config.log[file].level,
rewriters: [
(level, msg, meta) => {
meta.app = 'myApp';
return meta;
}
],
transports: [
/*your transports*/
]
});
For Winston v3:
const addAppNameFormat = winston.format(info => {
info.appName = "My Program";
return info;
});
const logger = winston.createLogger({
format: winston.format.combine(
addAppNameFormat(),
winston.format.json()
),
transports: [new winston.transports.Console()]
});
logger.warn('Danger Will Robinson!');
// {"message":"Danger Will Robinson!","level":"warn","appName":"My Program"}
See:
There is now (8/20/19) a property defaultMeta that is passed to createLogger that will inject the meta you specify to every log.
const logger = winston.createLogger({
level: 'info',
format: winston.format.json(),
defaultMeta: { service: 'user-service' },
transports: [
//
// - Write to all logs with level `info` and below to `combined.log`
// - Write all logs error (and below) to `error.log`.
//
new winston.transports.File({ filename: 'error.log', level: 'error' }),
new winston.transports.File({ filename: 'combined.log' })
]
});
There's no built-in way to do this, but you can definitely add it yourself - here's how:
First, set up your logger like you normally would. For example:
var logger = new (winston.Logger)({
"exitOnError" : true,
"transports" : [
new (winston.transports.Console)({ "colorize" : true, "level" : "silly", "silent" : false, "handleExceptions" : false }),
]
});
Then override the log() method (this is always called by the level methods - logger.foo() actually calls logger.log('foo').)
logger.log = function(){
var args = arguments;
if(args[2]) args[3] = args[2];
args[2] = {
"foo" : "bar"
}
winston.Logger.prototype.log.apply(this,args);
}
All I'm doing above is making it so when logger.log() is called, it instead calls the above method, which adds the metadata (in this case, an object containing a foo key). Then it calls winston's Logger.log method from the proper context.
The above code would be in a module you create, at the bottom just export the logger:
module.exports = logger;
and import the logger module instead of the winston module in your sub classes.
var logger = require('./logger.js');
Hope that helps!
Another option with an output more like log4j(s):
There is a documented label property which will add a label to the output (json or line):
var _ = require('lodash');
var winston = require('winston');
var path = require('path');
var baseDir = path.resolve(__dirname, '..');
// SETUP WINSTON LOGGER
var container = new winston.Container();
container.add("exception", {
console: {
handleExceptions: true,
timestamp: true,
label: "EXCEPTION",
colorize: true
}
});
container.get("exception").exitOnError = false;
var keys = [];
module.exports = function(filename) {
var label = path.relative(baseDir, filename);
if (!_.contains(keys, label)) {
container.add(label, {
console: {
handleExceptions: false,
level: 'debug',
timestamp: true,
label: label,
colorize: true
}
});
keys.push(label);
}
var logger = container.get(label);
logger.exitOnError = false;
return logger;
};
And in the other modules require it like this:
var logger = require('./logger')(__filename);
Example output:
2014-07-23T07:05:27.770Z - info: [config/config.js] .......
I was looking for a way to add the github delivery ID to all my logs.
I use winston 3 and defaultMeta getters along with express-http-context
// logger.js
const logger = (filename) => winston.createLogger({
...
defaultMeta: {
get deliveryId () { return httpContext.get('deliveryId'); },
get deliveryEvent () { return httpContext.get('deliveryEvent'); },
module: filename,
},
...
});
module.exports = (fileName) => {
return logger(fileName);
}
in my other modules:
// foo.js
const logger = require('./logger')(__filename)
module.exports = async(someInput) => {
logger.debug('hello ' + someInput)
}
I've found a better way using util-extend based on what I read on this blog. It will append the data in all cases, which I found useful for catching logger.info vs logger.log("info", message) and won't overwrite your other arguments.
logger.log = function(){
var args = arguments;
var level = args[0];
var newArgs = {
foo: "bar",
baz: "abc"
};
var originalMeta = args[2] || {};
args[2] = extend(originalMeta, newArgs);
winston.Logger.prototype.log.apply(this,args);
};
Will output in the console and in your logs.
Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.
