Ambil berurutan dan 5 cara untuk menyelesaikannya

Pada wawancara teknis, selain memeriksa pengetahuan teoretis, sudah lazim untuk mengatur tugas untuk menilai tingkat pengetahuan praktis kandidat, kemampuannya menulis kode, dan kemampuan berpikir logis dan algoritmik. Seringkali, daftar ini mencakup masalah algoritmik. Semua orang sudah terbiasa dengan mereka dan, ketika mempersiapkan, pertama-tama, mereka melihat mereka dengan tepat. Daftarnya panjang, tetapi hal utama yang paling sering ditemukan terlihat seperti ini:

• faktorial
• Angka-angka Fibonacci
• keunikan elemen array
• memeriksa tanda kurung di dalam teks
• (mergeSort, insertionSort, bubbleSort, quickSort)
• ( / / )

, 70 JavaScript, , , , ( , ).

, :

, , .

:

, :

:
fetch(url1) => fetch(url2, resultsUrl1) => fetch(url3, resultsUrl2)

-
compose(res2 => fetch(url3, res2), res1 => fetch(url2, res1), () => fetch(url1))

?

, ( ):

• async/await

, , ( reduce, ).

, ; , - ; ; .

, . . , , , .

, reduce , Array. :

• reduce

, fetch , :

function fakeFetch (url, params='-') {
    //           
    console.log(`fakeFetch to: ${url} with params: ${params}`);
    return new Promise(resolve => {
        setTimeout(() => resolve(`${url} is DONE`), 1000);
    })
};

( ):

const urls = ['url1', 'url2', 'url3'];

( 1), . then().then().then() await; await; await; .

, callback. :

fetchSeries(result => console.log(`result: ${result}`))

, . , , .

, , . , , , .

function generatorWay(callback) {
    function* generateSequence() {
        let results;
        for (let i = 0; i < urls.length; i++) {
            results = yield fakeFetch(urls[i], results);
        }
        return results;
    }
    function execute(generator, yieldValue) {
        let next = generator.next(yieldValue);
        if (!next.done) {  
            return next.value
                .then(result => execute(generator, result));
        } else {
            callback(next.value);
        }
    }
    execute(generateSequence())
}

:

• generateSequence yield' , .
• execute(generator), next, — , , , next.
• execute , callback.

, while:

async function asyncGeneratorWay(callback) {
    async function* generateSequence() {
        let results;
        for (let i = 0; i < urls.length; i++) {
            results = yield await fakeFetch(urls[i], results);
        }
        return results;
    }
    let generator = generateSequence();
    let result;
    while (!result || !result.done) {
        result = await generator.next(result && result.value);
    }
    callback(result.value);
}

( ).

for await of , 2.

Async/await

. , async/await. , async, .

async function asyncAwaitWay(callback) {
    const series = async () => {
        let results;
        for (let i = 0; i < urls.length; i++) {  
            results = await fakeFetch(urls[i], results);
        }
        return results;
    }
    const result = await series();
    callback(result);
}

fakeFetch await;

Recursion

, reduce ( ), recursion . . , :

function recursionWay(callback) {  
    const recursion = (arr = [], promise = Promise.resolve()) => {
        if (!arr.length) { 
            return promise;
        }
        const [url, ...restUrls] = arr;
        return promise
            .then(res => recursion(restUrls, fakeFetch(url, res)));
    }
    recursion(urls)
        .then(result => callback(result));
}

shift , . .

Promise.resolve(), -, , , .

Reduce

, , . , , .

function reduceWay(callback) {
    urls
        .reduce((accum, item) => {
            return accum
                .then(res => fakeFetch(item, res))
        }, Promise.resolve())
        .then(result => callback(result));
}

:

• fakeFetch then;
• , Promise.resolve(), -, , (Promise) , . :

function reduceWay(callback) {
    urls
        .reduce((accum, item) => {
            if (!accum) {
                return fakeFetch(item);
            }
            return accum
                .then(res => fakeFetch(item, res));
        })
        .then(result => callback(result));
}

2 .

. , :

"", , reduce. , ( ). , , :

const reduceWay = callback => urls.reduce(
    (acc, item) => acc.then(res => fakeFetch(item, res)),  
    Promise.resolve())
    .then(result => callback(result));  
}

, , , .

, — . async/await — , . reduce / .

, , … .

Generator

Generator Asinkron

Array: iterate over less

Pengulangan

Async / tunggu

Janji

Rantai Janji

UPD Saya membuat beberapa penyesuaian pada metode async / wait, mengikuti komentar. Memang, seseorang dapat mempersingkat metode dan memberikan visibilitas yang lebih besar dengan for of:

async function asyncAwaitWay(callback) {
    let results;
    for (const url of urls) {  
        results = await fakeFetch(url, results);
        }
    callback(result);
}