Following is the code to increment or decrement a variable on keyboard up/down press in JavaScript −
Example
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>>Document</title>
<style>
body {
font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
}
.result {
font-size: 20px;
font-weight: 500;
}
</style>
</head>
<body>
<h1>Changing variable value on keyboad up/down keypress</h1>
<div style="color: green;" class="result"></div&g;
<h3>
Press up or down arrow key to increment/decrement variable
</h3>
<script>
let dayVal = document.querySelector(".day");
let resEle = document.querySelector(".result");
let a = 0;
resEle.innerHTML = a;
document.body.addEventListener("keydown", (event) => {
if (event.keyCode === 38) {
resEle.innerHTML = ++a;
}
else if (event.keyCode === 40) {
resEle.innerHTML = --a;
}
});
</script>
</body>
</html>Output
The above code will produce the following output −
On pressing up arrow key a couple of times −
On pressing down arrow key a few times −
