Detecting arrow key presses in JavaScript

On key up and down call function. There are different codes for each key.

document.onkeydown = checkKey;

function checkKey(e) {

    e = e || window.event;

    if (e.keyCode == '38') {
        // up arrow
    }
    else if (e.keyCode == '40') {
        // down arrow
    }
    else if (e.keyCode == '37') {
       // left arrow
    }
    else if (e.keyCode == '39') {
       // right arrow
    }

}

Arrow keys are only triggered by onkeydown, not onkeypress.

The keycodes are:

• left = 37
• up = 38
• right = 39
• down = 40

Possibly the tersest formulation:

document.onkeydown = 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;
    }
};

Demo (thanks to user Angus Grant): http://jsfiddle.net/angusgrant/E3tE6/

This should work cross-browser. Leave a comment if there is a browser where it does not work.

There are other ways to get the key code (e.which, e.charCode, and window.event instead of e), but they should not be necessary. You can try most of them out at http://www.asquare.net/javascript/tests/KeyCode.html. Note that event.keycode does not work with onkeypress in Firefox, but it does work with onkeydown.

event.key === "ArrowRight"...

More recent and much cleaner: use event.key. No more arbitrary number codes! If you are transpiling or know your users are all on modern browsers, use this!

node.addEventListener('keydown', function(event) {
    const key = event.key; // "ArrowRight", "ArrowLeft", "ArrowUp", or "ArrowDown"
});

Verbose Handling:

switch (event.key) {
    case "ArrowLeft":
        // Left pressed
        break;
    case "ArrowRight":
        // Right pressed
        break;
    case "ArrowUp":
        // Up pressed
        break;
    case "ArrowDown":
        // Down pressed
        break;
}

Modern Switch Handling:

const callback = {
    "ArrowLeft"  : leftHandler,
    "ArrowRight" : rightHandler,
    "ArrowUp"    : upHandler,
    "ArrowDown"  : downHandler,
}[event.key]
callback?.()

NOTE: The old properties (.keyCode and .which) are Deprecated.

"w", "a", "s", "d" for direction, use event.code

To support users who are using non-qwerty/English keyboard layouts, you should instead use event.code. This will preserve physical key location, even if resulting character changes.

event.key would be , on Dvorak and z on Azerty, making your game unplayable.

const {code} = event
if (code === "KeyW") // KeyA, KeyS, KeyD

Optimally, you also allow key remapping, which benefits the player regardless of their situation.

P.S. event.code is the same for arrows

key Mozilla Docs

code Mozilla Docs

Supported Browsers