I've implemented an easily portable library on top of MooTools for writing arbitrarily nested AJAX requests without requiring callbacks of any kind. Long story short, Promises can be composed, AJAX requests cannot.
Instead of:
var result = '';
get('a', function(response) {
result += JSON.decode(response).data;
get('b', function(response) {
result += JSON.decode(response).data;
get('c', function(response) {
result += JSON.decode(response).data;
get('d', function(response) {
result += JSON.decode(response).data;
get('e', function(response) {
result += JSON.decode(response).data;
get('f', function(response) {
result += JSON.decode(response).data;
console.log(result);
});
});
});
});
});
});
function example()
{
var resources = ['a', 'b', 'c', 'd', 'e', 'f'];
var result = "";
while(resource = resources.shift())
{
result = add(result, get(resource));
}
show(result); // -> abcdef
}