Package Exports

ts-log
ts-log/build/src/index.js

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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 (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)