Listener/Observable based lazy async. It holds onto a function until it has been fulfilled, then it holds onto the captured response so that any future subscribers are also notified (in a lazy way). This is stateful in many ways and can be used for a generator in Streams and Promises in squishy-pants or similar libraries.

lazyAsync.js

function lazyAsync(f) {
    var args = [].slice.call(arguments).slice(1),
        listeners = [],
        captured;
    
    f.apply(null, [
        function() {
            captured = [].slice.call(arguments);
            for(var i = 0, total = listeners.length; i < total; i++) {
                listeners[i].apply(null, captured);
            }
            listeners.length = 0;
        },
        function() {
            listeners.length = 0;
        },
        args
    ]);
    
    return function(f) {
        if (captured) f.apply(null, captured);
        else listeners.push(f);
    };
}

var async = lazyAsync(
    function(resolve, reject, args) {
        setTimeout(function() {
            resolve(args[0]);
        }, 100);
    },
    1
);

async(
    function() {
        console.log('Finish 1', arguments);
    }
);
async(
    function() {
        console.log('Finish 2', arguments);
    }
);

setTimeout(
    function() {
        async(
            function() {
                console.log('Finish 3', arguments);
            }
        );
    }, 
    500
);