A useful little unless function written in javascript.

Unless.js

/**!
 * Unless
 * @created April 2013 by @jasonhowmans
 */
var unless = function( condition, callback ) {
    if (typeof callback === 'function') {
        if (!condition) callback();
    }else{
        return !condition;    
    }
};

Here's a fiddle with a really basic test case: http://jsfiddle.net/jasonhowmans/VMLYE/3/