A goofy, async, incomplete implementation of unless

unless.js

/**
 * user-space unless, some syntactic sugar from ruby implemented in JS
 * @var {bool} statement - any statement in JS that evaulates to a boolean. Watch for truthiness here.
 * @var {function} callback - adds the shiny sheen of async programming to this.
 */
window.unless = function(statement, callback) {
    var returnValue = false;
    args = [].slice.call(arguments);
    
    if (args.length > 2) {    
        callback = args.pop();
        if (typeof(callback) !== 'function') {
            throw "last argument really needs to be callable";
        }
    
        for(i in args) {
            if (!args[i]) { returnValue = true;
                // short-circuit. the first statement that evaluates as false breaks the chain
                break; 
            }
        }
    }
    else {
        // inversion, because this is *unless*
        (!statement) ? returnValue = true : returnValue = false;
    }
    if (returnValue === true) {
        callback(returnValue);
    }
}

// simple test
unless(2+2==5, function(val) {
    // we only get here if 2 + 2 = 5
    alert(val);
});

// simple test 2
unless(true, function(val) {
    // we always get here
    alert(val);
});

/**
 * Obvious limitations - no 'else' like in ruby, but IMHO doing unless .. else is really
 * bullshit anyway. You should just do if ... else. see this:
 *  http://railstips.org/blog/archives/2008/12/01/unless-the-abused-ruby-conditional/
 */