The order of events related to the keydown event:

keydown - The key is on its way down

The keydown event occurs when a keyboard key is pressed down.

The keydown() method triggers the keydown event, or attaches a function to run when a keydown event occurs.

Syntax:

$(selector).keydown() - Trigger the keydown event for the selected elements. 

$(selector).keydown(function) - Attach a function to the keydown event. 

Example:

<!doctype html>
	<html lang="en">
		<head>
		<meta charset="utf-8">

		<script src="https://code.jquery.com/jquery-3.4.1.js"></script>
		<script>  
		$(document).ready(function(){  
		    $("input").keydown(function(){  
				$("input").css("background-color", "green");  
		    });  
		    $("input").keyup(function(){  
				$("input").css("background-color", "violet");  
		    });  
		});  
		</script>   
		</head>
		<body>
			Write Anything: <input type="text">  
		</body>
	</html>

Keyup occurs when we release a key and Keydown occurs when we press a key on keyboard.