Александр

const timestamp = (year, month = 1, day = 1) => new Date(year, month - 1, day).getTime();

const entries = [
	{
		type: 'error',
		date: timestamp(2020, 4, 30)
	},
	{
		type: 'log',
		date: timestamp(2020, 4, 29)
	},
	{
		type: 'info',
		date: timestamp(2020, 4, 25)
	}
];

const date = new Date();
const today = timestamp(date.getFullYear(), date.getMonth() + 1, date.getDate());
const interval = 24 * 60 * 60 * 1000;

const entry = entries.find(entry => (entry.date >= today && entry.date <= today + interval));

console.log(entry); // { type: 'error', date: 1588183200000 }

window.addEventListener('scroll', event => {
  if (scrollY + innerHeight === document.body.scrollHeight) {
    // Code here
  }
});

const $humans = await data.response.items;

if($humans.some(entry => entry.hasOwnProperty('last_seen'))) {
    // Всё еще массив, так что надо еще найти тот элемент, в котором есть этот ключ
} else {
    // Всё еще массив
}

const $humans = await data.response.items;
const $human = $humans.find(entry => entry.hasOwnProperty('last_seen'));

if($human !== undefined) {
    // Первый элемент из массива с ключём last_seen
} else {
    // Какой-то код
}

Widget with id and

const sentence = 'Widget with id and';
const words = sentence.match(/\w+/g); // ['Widget', 'with', 'id', 'and']
console.log(words.indexOf('id'));

const apps = {
    site: true,
    blog: true,
    photos: false,
    shop: false
};

for (const app in apps) {
    if (apps[app] === true) {
        paths[app] = {
            views: {
                src: `./${app}/views/**/*.html`
            }
        };
    }
}

const values = [...document.querySelectorAll('[data-name]')].map(entry => entry.dataset.name);

grid-template-columns: 20% 60% 20%;
grid-template-columns: 2fr 6fr 2fr;
grid-template-columns: 1fr 3fr 1fr;

btn.textContent = btn.classList.contains('show')
    ? 'Скрыть'
    : 'Показать';

const date = new Date();
const time = Math.floor(date.getTime() / 1000);
const $1day = 24 * 60 * 60;
const filtered = array.filter(entry => {
  if (entry.hasOwnProperty('last_seen')) {
    return entry.last_seen.time > (time - $1day);
  }
  return false;
});

<button type="button" class="close" aria-label="Close">...</button>

const alerts = document.querySelectorAll('.alert');

for (const alert of alerts) {
  const closeButton = alert.querySelector('.close');

  if (closeButton !== null) {
    closeButton.addEventListener('click', event => {
      event.preventDefault();

      alert.style.setProperty('display', 'none');
    });
  }
}

computed: {
  sortedPersons: function () {
    return [...this.persons].sort((a, b) => a.age - b.age);
  }
}