class_2.js

class Stream {
    #value;
    #nextValue;

    static #count = 0;

    constructor(value, nextValue) {
        this.#value = value;
        this.#nextValue = nextValue;
        Stream.#count++;
    }

    get value() {
        return this.#value;
    }

    get next() {
        this.#value = this.#nextValue(this.#value);
        return this.#value;
    }

    static get count() {
        return Stream.#count;
    }
}

class ConstantStream extends Stream {
    constructor(value) {
        super(value, value => value);
    }
}

class NextIntegerStream extends Stream {
    constructor() {
        super(0, value => value + 1);
    }
}

const constant = new ConstantStream(0);
const nextInteger = new NextIntegerStream();

for (let i = 0; i < 10; i++) {
    console.log(`constant[${i}] = ${constant.next}`);
    console.log(`nextInteger[${i}] = ${nextInteger.next}`);
}