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

``cmd
npm install ts-log
`
`cmd
yarn add ts-log
`

Example

`typescript
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)