range.js

/**
 * @typedef {Object} RangeOpts
 * @property {number} [step=1]
 * @property {boolean} [isInclusive=2]
 */

class Range {
  #index = 0;
  #length = 0;

  /**
   * @param {number} start
   * @param {number} end
   * @param {RangeOpts} options
   */
  constructor(start, end, { step = 1, isInclusive = true } = {}) {
    switch (true) {
      case !Number.isInteger(step) || step === 0: throw new RangeError("step value must be a non-zero positive or negative integer");
      case start < end && Math.sign(step) === -1: throw new RangeError("step value must be positive for an ascending range");
      case start > end && Math.sign(step) === +1: throw new RangeError("step value must be negative for a descending range");
    }

    this.start = start;
    this.end = end;
    this.step = step;
    this.isIncusive = isInclusive;

    this.#length = Math.ceil((this.end - this.start) / this.step) + Number(this.isInclusive);
  }
  
  [Symbol.iterator]() {
    return this;
  }

  next() {
    if (this.#index === this.#length) return { done: true };
    
    const value = this.#index * this.step + this.start;
    this.#index++;
    return { value, done: false };
  }
}