A jQuery utility leveraging the Deferred Class to execute a code block in the future after a given condition is meet. See blog post for more: http://wp.me/p2kCXW-35

jQuery.doWhen.js

/*! Copyright (c) 2014 - Paul Tavares - purtuga - @paul_tavares - MIT License */
;(function($){
    
    /**
     * Delays the execution of a function until an expression returns true.
     * The expression is checked every 100 milliseconds for as many tries 
     * as defined in in the attempts option
     * 
     * @param {Object} options
     * @param {Function} options.when
     *                      Function to execute on every interval.
     *                      Must return true (boolean) in order for
     *                      options.do to be executed.
     * @param {Function} [options.exec]
     *                      Function to be executed once options.when()
     *                      returns true.
     * @param {Interger} [options.interval=100]
     *                      How long to wait in-between tries.
     * @param {Interger} [options.attempts=100]
     *                      How many tries to use before its considered
     *                      a failure.
     * @param {Interger} [options.delayed=0]
     *                      Number of miliseconds to wait before execution
                            is started. Default is imediately. 
     * 
     * @return {jQuery.Promise}
     * 
     * @example 
     * 
     *      $.doWhen({
     *          when: function(){
     *              return false;
     *          },
     *          exec: function(){
     *              alert("never called given false response on when param!");
     *          }
     *      })
     *      .fail(function(){
     *          alert('ALERT: FAILED CONDITION');
     *      })
     *      .then(function(){
     *          alert("resolved.");
     *      }); 
     * 
     */
    $.doWhen = function(options) {
        
        return $.Deferred(function(dfd){
            
            var opt = $.extend({}, {
                    when:       null,
                    exec:       function(){},
                    interval:   100,
                    attempts:   100,
                    delayed:    0
                },
                options,
                {
                    checkId: null
                }),
                startChecking = function(){
                    
                    // Check condition now and if true, then resolve object
                    if (opt.when() === true) {
                        
                        opt.exec.call(dfd.promise());
                        dfd.resolve();
                        return;
                        
                    }
                    
                    // apply minimal UI and hide the overlay
                    opt.checkId = setInterval(function(){
                            
                            if (opt.attempts === 0) {
                                
                                clearInterval(opt.checkId);
                                dfd.reject();
                                
                            } else {
                                
                                --opt.attempts;
                                
                                if (opt.when() === true) {
                                    
                                    opt.attempts = 0;
                                    clearInterval(opt.checkId);
                                    opt.exec.call(dfd.promise());
                                    dfd.resolve();
                                    
                                }
                                
                            }
                            
                        }, opt.interval);
                    
                };
             
            if (opt.delayed > 0) {
                
                setTimeout(startChecking, Number(opt.delayed));
                
            } else {
                
                startChecking();
                
            }
            
        }).promise();
        
    }; 

})(jQuery);