arrow keys function javascript

                                    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
    }

}

                                    
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;
    }
});
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
    }

}

                                    // Traditional Function Expression
var add = function(a,b){
  return a + b;
}

// Arrow Function Expression
var arrowAdd = (a,b) => a + b;