function Future(promise){
    var result;
    promise.then(function(res){
        result = res;
    });
    Object.defineProperties(this, {
        value: {
            get: function(){
                return result;
            }
        }
    });
}

var a = new Promise(function(resolve, reject){
    setTimeout(function(){resolve('Hello, Future');}, 500);
});
var b = new Future(a);
console.log('first call: %s', b.value);
setTimeout(function(){
    var c = b.value;
    console.log(c);
}, 1000);
console.log('second call: %s', b.value);