Example of iterable iterators and async iterable iterators on TypeScript

index.ts

/**
 * A silly class wrapping a number to demonstrate any type of object can be used
 * when using IterableIterators and how to use the 'n' value when iterating over
 * them.
 */
class SpecialNumber {
  private root: number;

  constructor(root: number) {
    this.root = root;
  }

  above() {
    return this.root + 1;
  }

  below() {
    return this.root - 1;
  }
}

/**
 * This class implements both the 'Symbol.asyncIterator' and the
 * 'Symbol.iterator' to show how to create iterable classes in TypeScript.
 *
 * This example was built with TypeScript 4.5.2. Not sure how far back in
 * versions compatibility goes.
 */
class IterableClass {
  private data: SpecialNumber[];

  constructor(data: number[]) {
    this.data = data.map((n) => new SpecialNumber(n));
  }

  /**
   * This will let us iterate this class with the 'for await .. of' syntax.
   * No need to implement any interface on the class.
   * The '*' after the 'async' keyword allows us to use 'yield' inside this method.
   */
  async *[Symbol.asyncIterator](): AsyncIterableIterator<SpecialNumber> {
    for (const n of this.data) {
      yield await new Promise((res) => setTimeout(res, 250, n));
    }
  }

  /**
   * This will let us iterate this class with the 'for .. of' syntax.
   * No need to implement any interface on the class.
   * The '*' allows us to use 'yield' inside this method.
   */
  *[Symbol.iterator](): IterableIterator<SpecialNumber> {
    for (const n of this.data) {
      yield n;
    }
  }

  getName(): SpecialNumber[] {
    return this.data;
  }
}

(async () => {
  const t = new IterableClass([1, 2, 3]);

  // in this case, 'n' is of type 'SpecialNumber', so we can call any of its methods
  for await (const n of t) {
    console.log({ n: n.above() });
  }

  console.log('in between for loops');

  // the same applies here
  for (const n of t) {
    console.log({ n: n.above() });
  }
})();