Package Exports

ts-log

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Readme

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.

Matches the build-in console that can be directly plugged in.
Also matches bunyan.
Provides usage and custom logger example.
Written in TypeScript, no need for extra typings.

Installation

This package is distributed via npm

npm install ts-log

Example

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

// example custom logger that logs to a file
class FileLogger implements ILogger {
  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`);
  }
}

// example class that uses the logger
class Calculator {
  // accept the logger in the constructor, defaulting to dummy logger
  public constructor(private readonly log: ILogger = 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;
  }
}

// don't define the logger, defaults to dummy logger that does not do anything
const calculator1 = new Calculator();

// use the build-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

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