TypeScript Abstract Logger

Abstract logger TypeScript interface along with a dummy logger that does nothing.

Useful for libraries wanting to provide a pluggable logger that does nothing by default (or provide your own default such as bunyan).

• Matches the built-in console that can be used directly.
• Also matches bunyan.
• Provides usage and custom logger example.
• Written in TypeScript, no need for extra typings.
• No dependencies, 24 LOC with comments, 100% test coverage.

Installation

This package is distributed via npm

npm install ts-log

yarn add ts-log

Example

import { dummyLogger, Logger } from "ts-log";
import * as fs from "fs";

// example class that uses the logger
class Calculator {
  // accept the logger in the constructor, defaulting to dummy logger that does nothing
  public constructor(private readonly log: Logger = dummyLogger) {}

  public sum(a: number, b: number) {
    const result = a + b;

    // call the logger
    this.log.info(`summing ${a} + ${b} = ${result}`, a, b, result);

    return result;
  }
}

// example custom logger that logs to a file
class FileLogger implements Logger {
  private readonly fd: number;

  public constructor(filename: string) {
    this.fd = fs.openSync(filename, "a");
  }

  public trace(message?: any, ...optionalParams: any[]): void {
    this.append("TRACE", `${message} ${JSON.stringify(optionalParams)}`);
  }

  public debug(message?: any, ...optionalParams: any[]): void {
    this.append("DEBUG", `${message} ${JSON.stringify(optionalParams)}`);
  }

  public info(message?: any, ...optionalParams: any[]): void {
    this.append("INFO ", `${message} ${JSON.stringify(optionalParams)}`);
  }

  public warn(message?: any, ...optionalParams: any[]): void {
    this.append("WARN ", `${message} ${JSON.stringify(optionalParams)}`);
  }

  public error(message?: any, ...optionalParams: any[]): void {
    this.append("ERROR", `${message} ${JSON.stringify(optionalParams)}`);
  }

  private append(type: string, message: string) {
    fs.writeSync(this.fd, `${new Date().toISOString()} ${type} ${message}\n`);
  }
}

// don't define a logger, defaults to dummy logger that does nothing
const calculator1 = new Calculator();

// use the built-in console as the logger
const calculator2 = new Calculator(console);

// use the custom file logger
const calculator3 = new Calculator(new FileLogger("log.txt"));

// run the calculator
calculator1.sum(2, 3);
calculator2.sum(-4, 1);
calculator3.sum(6, 3);

Commands

• npm start to start the example application.
• npm run build to build the production version.
• npm run test to run tests.
• npm run coverage to gather code coverage.
• npm run lint to lint the codebase.
• npm run prettier to run prettier.
• npm run validate to run all pre-commit checks (prettier, build, lint, test)