node-Use promise, generator, async/await to read files

In node, the module for reading files is fs, which is divided into synchronous reading and asynchronous reading.

const fs = require('fs');

// Read files synchronously
let buf = fs.readFileSync('a.text');

//  Read files asynchronously
fs.readFile('a.text', (err, data) => {
    if (err) {
        console.log('Failed to read file');
    } else {
        console.log(data);
    }
});

In the development process of JavaScript, it has experienced callback functions, Promise objects, Generator functions, and async functions to handle asynchrony. Let's take a look at how the async function handles asynchronous more gracefully. Suppose we need to read three files a, b, and c respectively, the specific code is as follows:

Promise encapsulation of fs module

const readFile = function (src) {
    return new Promise((resolve, reject) => {
        fs.readFile(src, (err, data) => {
            if (err) reject(err);
            resolve(data);
        });
    });
};

Promise writing

readFile('a.text').then(data => {
    console.log(data.toString());
    return readFile('b.text');
}).then(data => {
    console.log(data.toString());
    return readFile('c.text');
}).then(data => {
    console.log(data.toString());
});

Generator's writing

function * ascReadFile () {
    yield readFile('a.text');
    yield readFile('b.text');
    yield readFile('c.text');
}

let g = ascReadFile();
g.next().value.then(data => {
    console.log(data.toString());
    return g.next().value;    
}).then(data => {
    console.log(data.toString());
    return g.next().value;   
}).then(data => {
    console.log(data.toString());
});

async function writing

async function asyncReadFile(){
    let a = await readFile('a.text');
    console.log(a.toString());

    let b = await readFile('b.text');
    console.log(b.toString());

    let c = await readFile('c.text');
    console.log(c.toString());
}

asyncReadFile();

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