A <non-generic & strictly-typed> collection of numbers in pure Javascript

NumberCollection.js

class NumberCollection {
  #numbers;

  constructor(numbers) {
    if (
      !Array.isArray(numbers) ||
      !numbers.every((str) => typeof str === "number")
    ) {
      throw new Error(
        "NumberCollection should be initialized with an array of numbers"
      );
    }
    this.#numbers = numbers;
  }

  [Symbol.iterator]() {
    let index = 0;
    let numbers = this.#numbers;

    return {
      next: function () {
        if (index < strings.length) {
          return { value: numbers[index++], done: false };
        } else {
          return { done: true };
        }
      },
    };
  }

  toJSON() {
    return this.#numbers;
  }
}