Keyboard navigation for Fingerpori @ Turun Sanomat using (jQuery) promises

ts-fp-kbdnav.js

// Keyboard navigation for http://ts.fi/viihde/fingerpori/
(function ($) {
    "use strict";

    if (!$) {
        console.error("jQuery is missing");
        return;
    }

    var KEYS = {
        ARROW_LEFT: 37,
        ARROW_RIGHT: 39,
        ARROW_UP: 38,
        ARROW_DOWN: 40,

        // Store interesting keycodes for quick lookup
        VALID: [37, 39, 38, 40]
        };

    function identifyActor(kc) {
        var actor = null;
        
        switch (kc) {
            case KEYS.ARROW_RIGHT:
                actor = ".comic .comic-button-next";
                break;
                
            case KEYS.ARROW_LEFT:
                actor = ".comic .comic-button-prev";
                break;
                
            case KEYS.ARROW_DOWN:
                actor = "#comic-serie-container .comic-button-next";
                break;
                
            case KEYS.ARROW_UP:
                actor = "#comic-serie-container .comic-button-prev";
                break;
        }
        
        return actor;
    }
    
    function navigate(e) {
        var actor, fetch;

        if (KEYS.VALID.indexOf(e.keyCode) === -1) {
            return;
        }

        e.preventDefault();
        e.stopPropagation();

        // Create actor promise
        actor = $.when(identifyActor(e.keyCode)).
        then(function (actor) {            
            return $(actor);
        });
        
        // Create fetch promise
        fetch = actor.
        then(function ($actor) {
            return $actor.attr("href");
        }).
        then(function (url) {
            return $.get(url);
        });
        
        // Then wait until both resolve
        $.when(actor, fetch).
        then(function (actor, fetch) {
            return $(actor.data("ajaxUpdate")).html(fetch[0]);
        }, function (err) {
            console.error("error", err);
        });
    }    
    
    $(window).on("keydown", navigate);
}(jQuery));