function jsonPost(url, data) {
	return new Promise((resolve, reject) => {
		const x = new XMLHttpRequest();
		x.onerror = () => reject(new Error('jsonPost failed'))
		//x.setRequestHeader('Content-Type', 'application/json');
		x.open("POST", url, true);
		x.send(JSON.stringify(data))

		x.onreadystatechange = () => {
			if (x.readyState === XMLHttpRequest.DONE && x.status === 200){
				resolve(JSON.parse(x.responseText))
			} else if (x.status !== 200){
				reject(new Error('status is not 200'))
			}
		}
	});
}

const url = "http://students.a-level.com.ua:10012";

let messagesArray = jsonPost(url, {func: 'getMessages'});

const addZero = data => data < 10 ? `0${data}` : data;

const buildDate = date => `${date.getDate()}/${date.getMonth()+1}/${date.getFullYear()} ${addZero(date.getHours())}:${addZero(date.getMinutes())}:${addZero(date.getSeconds())}`;

const buildMessage = (nick, message, time) => {
  return `<p>nick - ${nick}, message - ${message}, date - ${buildDate(new Date(time))}</p>`;
}

messagesArray.then(messages => {
	for (const message of messages.data) {
		chatMessages.insertAdjacentHTML('afterbegin', buildMessage(message.nick, message.message, message.timestamp));
	}
});