Mã hoàn chỉnh của lịch bằng JavaScript

Mã hoàn chỉnh của tôi tại thời điểm này:

<div id="parent">
	<div id="calendar">
		<table>
			<thead>
				<tr>
					<th>Thứ 2</th>
					<th>Thứ 3</th>
					<th>Thứ 4</th>
					<th>Thứ 5</th>
					<th>Thứ 6</th>
					<th>Thứ 7</th>
					<th>Chủ nhật</th>
				</tr>
			</thead>
			<tbody class="body"></tbody>
		</table>
	</div>
</div>

#parent {
	text-align: center;
}
#calendar {
	display: inline-block;
}
#calendar td, #calendar th {
	padding: 5px 12px;
	border: 1px solid black;
	text-align: center;
}

let calendar = document.querySelector('#calendar');
let body = calendar.querySelector('.body');
let prev = calendar.querySelector('.prev');
let next = calendar.querySelector('.next');

let date  = new Date();
let year  = date.getFullYear();
let month = date.getMonth();

draw(body, year, month);

function draw(body, year, month) {
	let arr = range(getLastDay(year, month));
	
	let firstWeekDay = getFirstWeekDay(year, month);
	let lastWeekDay  = getLastWeekDay(year, month);
	
	let nums = chunk(normalize(arr, firstWeekDay, 6 - lastWeekDay), 7);
	createTable(body, nums)
}

function createTable(parent, arr) {
	parent.textContent = '';
	let cells = [];
	
	for (let sub of arr) {
		let tr = document.createElement('tr');
		
		for (let num of sub) {
			let td = document.createElement('td');
			td.textContent = num;
			tr.appendChild(td);
			
			cells.push(td);
		}
		
		parent.appendChild(tr);
	}
	
	return cells;
}

function normalize(arr, left, right) {
	for (let i = 0; i < left; i++) {
		arr.unshift('');
	}
	for (let i = 0; i < right; i++) {
		arr.push('');
	}
	
	return arr;
}

function getFirstWeekDay(year, month) {
	let date = new Date(year, month, 1);
	let num  = date.getDay();
	
	if (num == 0) {
		return 6;
	} else {
		return num - 1;
	}
}

function getLastWeekDay(year, month) {
	let date = new Date(year, month + 1, 0);
	let num  = date.getDay();
	
	if (num == 0) {
		return 6;
	} else {
		return num - 1;
	}
}

function getLastDay(year, month) {
	let date = new Date(year, month + 1, 0);
	return date.getDate();
}

function range(count) {
	let arr = [];
	
	for (let i = 1; i <= count; i++) {
		arr.push(i);
	}
	
	return arr;
}

function chunk(arr, n) {
	let result = [];
	let count = Math.ceil(arr.length / n);
	
	for (let i = 0; i < count; i++) {
		let elems = arr.splice(0, n);
		result.push(elems);
	}
	
	return result;
}