document.getElementById('increase').addEventListener('click', increase);
И
<input class="btn" id="Increase" type="button" value="Increase">
Не соответствует
//selecting elements
let value = document.getElementById('value');
let counter = 0;
value.textContent = counter;
// addingEventListener
document.getElementById('reset').addEventListener('click', reset);
document.getElementById('Increase').addEventListener('click', increase);
document.getElementById('decrease').addEventListener('click', decrease);
// Event functions
function reset() {
counter = 0;
}
function increase() {
counter++;
}
function decrease() {
counter--;
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<div id="main">
<div class="container">
<p class="two-times">Counter</p>
<p class="two-times" id="value">0</p>
<div class="buttons">
<input class="btn" id="decrease" type="button" value="Recrease">
<input class="btn" id="reset" type="button" value="Reset">
<input class="btn" id="Increase" type="button" value="Increase">
</div>
</div>
</div>
<!-- javaScript -->
<script src="app.js"></script>
</body>
</html>