A simple way to keep track of which keys are pressed at any one time.

PressedKeys.js

var PressedKeys = function($elt) {
    var pressed = {};
    ($elt || $(document)).on('keydown keyup', function(evt) {
        pressed[evt.keyCode] = (evt.type == 'keydown');
    });
    return pressed;
};


// example
var pressedKeys = PressedKeys($('canvas.game'));
(function loop() {
    if (pressedKeys['39']) {
        // do something right
    } else if (pressedKeys['37'] {
        // do something left
    }
    window.setTimeout(loop, 80);
})();

@mrcoles Hello from 2024.

typo here:

} else if (pressedKeys['37'] {

should be:

} else if (pressedKeys['37']) {