Javascript keycode clash: “right arrow” and “single quote”

Question

The following script does what it should, that is, it reacts on the keys \"arrow left\" and \"arrow right\". However, due to a keycode clash, it reacts on a single quote as

Answer 1

When the user presses the single quote key, the e.keyCode property is zero, and the e.which property is 39. Executing String.fromCharCode(39) returns a single quote.

You want the keyCode if that property is in the event object:

var keycode = "keyCode" in e ? e.keyCode : e.which;

That way you get zero for the keyCode when that property exists in the event object, and when the which property also exists.

document.onkeydown = function(event) {
    event = event || window.event;

    var keyCode = "keyCode" in event ? event.keyCode : event.which;

    switch (keyCode) {
        case 37: console.log("37 was pressed", event); break;
        case 39: console.log("39 was pressed", event); break;
    }
};

Edit #1: Other commenters and answers are correct. I forgot you shouldn't be detecting control keys with keypress events. Changed to onkeydown.

Full HTML example that works cross browser: