v-logger

A customizable logger module written in Typescript. Extension of the logger is available as a koa logger middleware.

Basic Usage

const { logger } = require("v-logger");

logger.info("Hello world");

Customizing logging format and logging level:

logger.format("[:date] :name > :level: :msg");
logger.level("DEBUG");
logger.info("Another hi!");

or create your own logger with options and write logs to file:

const fs = require("fs");

const { Logger } = require("v-logger");
const myLogger = new Logger("MyLogger", { 
    format: "[:date] :name > :level: :msg",
    dateFormat: "iso",
    logLevel: "WARN",
    stream: fs.createWriteStream("warnings.log");
});
myLogger.info("This message will not be logged.");
myLogger.warn("This message will be logged.");

Log Levels

There are 6 pre-defined LogLevels, each associate with an integer value:

VERBOSE: 0;
DEBUG: 10;
INFO: 20;
WARN: 30;
ERROR: 40;
CRITICAL: 50;

You can customize your own LogLevel using:

LogLevel.addLevel("MY-LEVEL", 25);
logger.log("MY-LEVEL", "This is a log with custom log level.");

Options

Available options for customizing a logger instance:

• logLevel: the threshold LogLevel of the logger, all logs with lower level than this one would be emitted. Default to "INFO".

• format: a format template for logging, all tokens should start with a :.

  Available tokens for the basic logger are: date (the created date of a log record), name (the name of the logger), level (the level of a log record), msg (the message or content of the log).

• stream: a WritableStream to write the log to. Default to process.stdout.

• dateFormat: a format template for date. Pre-set formats are "iso" and "utc". To customize your own date format, please reference the following available tokens.

%%: A literal % character.

%a: Locale’s abbreviated weekday name.

%A: Locale’s full weekday name.

%b: Locale’s abbreviated month name.

%B: Locale’s full month name.

%c: Locale’s appropriate date and time representation.

%d: Day of the month as a decimal number [01,31].

%H: Hour (24-hour clock) as a decimal number [00,23].

%I: Hour (12-hour clock) as a decimal number [01,12].

%m: Month as a decimal number [01,12].

%M: Minute as a decimal number [00,59].

%P: Locale’s equivalent of either AM or PM.

%S: Second as a decimal number [00,59].

%w: Weekday as a decimal number [0(Sunday),6].

%x: Locale’s appropriate date representation.

%X: Locale’s appropriate time representation.

%y: Year without century as a decimal number [00,99].

%Y: Year with century as a decimal number.

%z: Time zone offset indicating time difference from UTC/GMT of the form +HHMM or -HHMM, where H represents decimal hour digits and M represents decimal minute digits [-23:59, +23:59].

Koa Logger Middleware

Create a koa logger middleware by:

import { koaLogger } from "v-logger";
import * as Koa from "koa";

const app = new Koa();
app.use(koaLogger("MyLogger"));
...

Customizing Logger Middleware

const options = {
    format: ':remote-addr [:date] ":method :url HTTP/:http-version" :status :length - :response-time ms',
    logLevel: "INFO",
    dateFormat: "utc",
};
app.use(koaLogger("MyLogger", options));