Class definitions

Originally to make classes, was used “prototype-based inheritance” when new functions were added into function prototype.

This was complex and brought a lot of confusion.

Staring from ECMAScript 2015 classes were introduced

type LogLevel = "error" | "debug";
class Logger {
  level: LogLevel;

  constructor(level: LogLevel) {
    this.level = level;
  }

  log(message: string) {
    console.log(`${this.level}: ${message}`);
  }
}

const logger = new Logger("debug");
logger.log("Test message");

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Try to use functional approaches always. Your code should not have class definitions, believe you don’t need them.

Inheritance in classes

class BaseLogger {
  name: string;
  constructor(prefix: string) {
    this.name = prefix;
  }
  getFullMessage(message: string) {
    return `${this.name}: ${message}`;
  }
}

class ExtendedLogger extends BaseLogger {
  constructor(name: string) {
    super(name); // call base class constructor
  }
  getFullMessage(message: string) {
    //call base version of `getFullMessage`
    return `Extended: ${super.getFullMessage(message)}`;
  }
}

const extendedLogger = new ExtendedLogger("SampleLog");
console.log(extendedLogger.getFullMessage("some message")); // Extended: SampleLog: some message

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Class members definition

class PublicPrivate {
  // public by default
  name0: string = "test";
  // private
  #name: string = "test";
  // private
  private name2 = "test3";
  // public
  public name3 = "test3";
  // readonly (public)
  readonly canBeSetInConstructorOnly: boolean;

  constructor() {
    this.canBeSetInConstructorOnly = true;
  }
  private get() {}
  set() {}
  i_am_using_all() {
    this.#name;
    this.name2 = `${this.name2}something`;
  }
}

const publicPrivate = new PublicPrivate();
publicPrivate.name0; // ok
publicPrivate.name3; // ok
publicPrivate.set(); // ok

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