ES6 Symbol / For-of / Iterator / Generator

01_Symbol.js

// --- //

const secret = Symbol();

const user = {
    id: 1,
    login: 'Vasya',
    [secret]: '45sdfgh6n'
};

console.log('user', user);

console.log('user.login', user.login);
console.log('user.secret', user.secret);
console.log('user[secret]', user[secret]);

// --- //

const secret = Symbol('secret');

const user = {
    id: 1,
    login: 'Vasya',
    [secret]: '45sdfgh6n'
};

console.log('user', user);

console.log('user.login', user.login);
console.log('user.secret', user.secret);
console.log('user[secret]', user[secret]);

// --- //

const symbol1 = Symbol();
const symbol2 = Symbol('foo');
const symbol3 = Symbol('foo');

console.log('symbol1', symbol1);
console.log('symbol2 == symbol3', symbol2 == symbol3);
console.log('symbol2 === symbol3', symbol2 === symbol3);
console.log('typeof symbol2', typeof symbol2);

02_For_Of.js

const arr = [1, 2, 3]

for (let i = 0; i < arr.length; i++) {
    console.log(arr[i])
}

// --- //

arr.forEach(function(value) {
    console.log(value)
})

arr.forEach(value => console.log(value))

// --- //

for (let i in arr) {
    console.log(arr[i])
}

// --- //

for (let value of arr) {
    console.log(value)
}

// --- //

for (let char of 'Hello') {
    console.log(char)
}

// --- //

let types = new Set(['foo', 'bar', 'foo', 'baz'])

for (let type of types) {
    console.log(type)
}

// --- //

let obj = { foo: 'bar', baz: 'aux' }

for (let type of obj) {
    console.log(type)
}

// --- //

let obj = { foo: 'bar', baz: 'aux' }

for (let key of obj.keys()) {
    console.log(obj[key])
}

// Array.prototype[Symbol.iterator] -> function(){...}
// Set.prototype[Symbol.iterator] -> function(){...}

03_Iterators.js

let iterator = {
    [Symbol.iterator]: function() {
        return this;
    },

    next: function() {
        return { done: false, value: 'hey' };
    }
}

// --- //

function createIterator(arr){
    let index = 0;
    
    return {
       next: () => {
           return index < arr.length
           ? { value: arr[index++], done: false }
           : { done: true };
       }
    }
}

const myIterator = createIterator(['hey', 'yo', 'ya']);

console.log( myIterator.next() );
console.log( myIterator.next() );
console.log( myIterator.next() );
console.log( myIterator.next() );
console.log( myIterator.next() );

04_Generators.js

function* countToThree() {
    yield 1;
    yield 2;
    return 3;
}

const counter = countToThree();

console.log( counter.next() );
console.log( counter.next() );
console.log( counter.next() );

// --- //

function* createCounter(start, end) {
    for (let i = start; i <= end; i++) {
        yield i;
    }
}

const counter = createCounter(1, 3);

console.log( counter.next() );
console.log( counter.next() );
console.log( counter.next() );

// --- //

function* counterOfCounters() {
    yield* createCounter(1, 3);

    yield* createCounter(6, 9);

    yield* createCounter(20, 22);
}

for (let count of counterOfCounters()) {
    console.log(count);
}

// --- //

function* fetchPost() {
    const request = yield fetch(`https://jsonplaceholder.typicode.com/posts/1`);

    const post = yield request.json();

    return post.body;
}

const iterator = fetchPost();

const promise = iterator.next().value;

promise.then(data => {
    const anotherPromise = iterator.next(data).value;

    anotherPromise.then(anotherData => {
        console.log(iterator.next(anotherData).value);
    })
})

// --- //

run(
    function* getHouseMembers(id) {
        const request = yield fetch(`http://anapioficeandfire.com/api/houses/${id}`);

        const { swornMembers: swornMemberURLs } = yield request.json();

        const swornMembers = [];

        for (let swornMemberURL of swornMemberURLs) {
            const swornMember = yield fetch(swornMemberURL);
            const swornMemberJson = yield swornMember.json();

            swornMembers.push(swornMemberJson);
        }

        return swornMembers;
    }
, 378).then(console.log).catch(console.error);

function run(generator, ...args) {
    const iterator = generator(...args);

    function iterate({ done, value }) {
        if (done) {
            return value;
        }

        return value.then(data => iterate(iterator.next(data)))
    }

    return iterate(iterator.next());
}

// --- //

function* fetchGenerator(url) {
    const request = yield fetch(url);

    const json = yield request.json();

    return json;
}

run(
    function* getHouseMembers(id) {
        const { swornMembers: swornMemberURLs } = yield* fetchGenerator(`http://anapioficeandfire.com/api/houses/${id}`);

        const swornMembers = [];

        for (let swornMemberURL of swornMemberURLs) {
            swornMembers.push(yield* fetchGenerator(swornMemberURL));
        }

        return swornMembers;
    }
, 378).then(console.log).catch(console.error);

function run(generator, ...args) {
    const iterator = generator(...args);

    function iterate({ done, value }) {
        if (done) {
            return value;
        }

        return value.then(data => iterate(iterator.next(data)))
    }

    return iterate(iterator.next());
}