Generators talk as part of UI Lunch and Learn 12/15/2022

generators.js

// Generators

const obj = {
  a: 1,
  b: 2,
  c: 3,
};

obj[Symbol.iterator] = function *() {
  for(const k of Object.keys(obj)) {
    yield [k, obj[k]]
  }
};
const iterObj = Object.keys(obj).map(x => [x, obj[x]]);

[...obj]

function* naturalNumbers() {
    for (let n=0;; n++) {
        yield n;
    }
} 

// const aa = naturalNumbers()
const [a, b, c] = naturalNumbers();
console.log({ a, b, c })

const squaredInts = function *() {
  let i = 1;
  while (true) {
    yield i * i;
    i += 1;
  }
}
const [d, e, f, g, h, i] = squaredInts();
console.log({ d, e, f, g, h, i});


function* take(n, iterable) {
    for (const x of iterable) {
        if (n <= 0) return;
        n--;
        yield x;
    }
} 

// function sumOfSquared(bound) {
//   const sqs = squaredInts();
//   let acc = 0;
//   for(const sq of sqs) {
//     // console.log({ sq })
//     acc += sq;
//     if (acc > bound) return acc;
//   }
// }

[...take(29, naturalNumbers())]
// sumOfSquared(33)

const str = 'Hello! this is @kesava demonstrating @javascript';
const usernameRegex = new RegExp(/@(\w+)/, 'g');
function *getUsernames(str) {
  let match = null;
  do {
    match = usernameRegex.exec(str);
    if (match) {
      yield match;
    }
  } while (match);
}

[...getUsernames(str)]

class BinaryTree {
  constructor(value, left=null, right=null) {
    this.value = value;
    this.left = left;
    this.right = right;
  }
  * [Symbol.iterator]() {
    if (this.left) {
      yield* this.left
    }
        yield this.value;

    if (this.right) {
      yield* this.right;
    }
  }
}

const tree = new BinaryTree(3, new BinaryTree(2), new BinaryTree(9, new BinaryTree(7), new BinaryTree(11)));
[...tree]