Function.prototype.promise = function () {
/* Arguments:
        condition to be met before running
        polling interval
        arguments for the function
*/
    var __method=this,
        oArgs=arguments,
        args=[],i,__cond=oArgs[0],__intv=oArgs[1];
    for (i=2; i<oArgs.length; i++) args.push(oArgs[i]);
    if (__cond.apply(__cond,args))
        this.apply(this,args);
    else window.setTimeout(function () {
        __method.promise.apply(__method,oArgs);
    },__intv*1000);
}

/* Very simplistic example of use */
function fnc(a) { //What we're promising to do
        alert(a)
}
//Dummy variable that's just not what we need it to be... yet
var valueToTrack=5;

//Make the promise
fnc.promise(
        function() {
                return valueToTrack==4; 
        },1,'I\'ve kept my promise'
);
// at some point in the future, the condition changes...
setTimeout("valueToTrack--;", 4000);