JS 2017

Promises

Best or Worse

a lot of API based on Promises

fetch

Response and Request

Headers and Body

https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API

What is the problem with fetch API?

Cancel

How do you cancel?

Tasks

toTask(getUser()
	.then(populateGroups)
	.then(checkDriver)
	.then(getTrips)
	.then(getAddresses)
).andThen(render)

Cancellation tokens

var { token, cancel } = CancelToken.source();

getUsers({}, token).then(render)

cancel();

async function getUsers (data, token) {
	var users = await getUsersFromDB(data, token);
	token.throwIfRequested();

	let fullUsers = await populateUsers(users, token);
	token.throwIfRequested();

	return fullUsers;
}

async function getUsers (data, token) {
        await.cancelToken = token;
	var users = await getUsersFromDB(data, token);
	let fullUsers = await populateUsers(users, token);
	return fullUsers;
}

Generators

Consumer vs Producer

What is a problem with generators

function* getLines () {
    var reader = new FileReader("Some.txt");

    while (!reader.oef) {
        let line = reader.readLine();
        yield JSON.parse(line);
    }

    reader.close();
    return "";
}

They are sync

We can't use them with WebSockets

async function* getLines () {
    var reader = new AsyncFileReader("Some.txt");

    while (!reader.oef) {
        let line = await reader.readLine();
        yield JSON.parse(line);
    }

    await reader.close();
}

var iterator = getLines();

iterator.next().then(() => {});
iterator.next().then(() => {});
iterator.next().then(() => {});
iterator.next().then(() => {});

for-of

for await(let line of getLine()) {
    // here is line
}

WebSockets and Node Streams

Observer

interface Observer<T> {
    next (data: T): void,
    error (e: Error): void,
    complete (data: T): void
}

interface Observable<T> {
    subscribe (obs: Observer<T>, cancelToken): { 
        unsubscribe (): void 
    }
}

What is also new?

DOM 4

forEach, entities, keys

passive, once events

https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener

append, prepend, remove, before, after, closest, contains, matches