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    2.2.4 • Public • Published

    TypeScript Abstract Logger

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    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.


    This package is distributed via npm

    npm install ts-log
    yarn add ts-log


    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`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);


    • 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)


    npm i ts-log

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    • kallaspriit