if(e.keyCode == 38) code example

Example 1: javascript detect arrow key press

//detecting arrow key presses
document.addEventListener('keydown', function(e) {
    switch (e.keyCode) {
        case 37:
            alert('left');
            break;
        case 38:
           alert('up');
            break;
        case 39:
            alert('right');
            break;
        case 40:
            alert('down');
            break;
    }
});

Example 2: js detect right key click

//detecting arrow key presses - supports both new and depricated methods
document.addEventListener('keydown', function(e) {
	var key = e.key || e.keyCode;
	switch (key) {
		case 'ArrowLeft': case 37:
			alert('left');
			break;
		case 'ArrowUp': case 38:
			alert('up');
			break;
		case 'ArrowRight': case 39:
			alert('right');
			break;
		case 'ArrowDown': case 40:
			alert('down');
			break;
	}
});

Example 3: keycode letters

0	48
1	49
2	50
3	51
4	52
5	53
6	54
7	55
8	56
9	57
a	65
b	66
c	67
d	68	
e	69
f	70
g	71
h	72
i	73
j	74
k	75
l	76
m	77
n	78
o	79
p	80
q	81
r	82
s	83
t	84
u	85
v	86
w	87
x	88
y	89
z	90