async example: (1) get file contents, (2) parse it as a json, (3) add sth, (4) serialize back to string, (5) send a e-mail

01-xmas-tree.js

function handleError (error) {}
function readFile (PATH, fail, win) {}
function parseJSON (DATA, fail, win) {}
function stringifyJSON (JSON, fail, win) {}
function sendMail (STRING, fail, win) {}

readFile(
    PATH,
    handleError,
    function (DATA) {
        parseJSON(
            DATA,
            handleError,
            function (JSON) {
                JSON.foo = 42;
                stringifyJSON(
                    JSON,
                    handleError,
                    function (STRING) {
                        sendMail(
                            STRING,
                            handleError,
                            function () {
                                console.log('at fscking last!');
                            }
                        );
                    }
                );
            }
        );
    }
);

02-promise.js

function handleError (error) {}

// all of these return Promise
function readFile (PATH) {}
function parseJSON (STRING) {}
function stringifyJSON (JSON) {}
function sendMail (STRING) {}

readFile(path)
    .then(parseJSON)
    .then(function (JSON) {
        JSON.foo = 42;
        return stringifyJSON(JSON);
    })
    .then(sendMail)
    .catch(handleError);

03-generators.js

function handleError (error) {}

// all of these return Promise
function readFile (PATH) {}
function parseJSON (STRING) {}
function stringifyJSON (JSON) {}
function sendMail (STRING) {}


function* doStuff (PATH)
{
    var VALUE;
    try
    {
        VALUE = yield readFile(PATH);
        VALUE = yield parseJSON(VALUE);
        VALUE.foo = 42;
        VALUE = yield stringifyJSON(VALUE);
        VALUE = yield sendMail(VALUE);
    }
    catch (error)
    {
        handleError(error);
    }
}

magic(doStuff);