以读取文件为例，首先，创建文件a.txt，文件内写入内容Hello world!。

回调函数写法

const fs = require('fs')
fs.readFile('./a.txt', 'utf-8', (err, data) => {
    if (err) throw err
    console.log(data)
})

Promise写法

const fs = require('fs')
function getTxt (path) {
    return new Promise((resolve, reject) => {
        fs.readFile(path, 'utf-8', (err, data) => {
            if (err) reject(err)
            resolve(data)
        })
    })
}
getTxt('./a.txt')
    .then(rst => console.log(rst))

bluebird写法

const Promise = require('bluebird')
const fs = Promise.promisifyAll(require('fs'))
fs.readFileAsync('./a.txt', 'utf-8')
    .then(data => console.log(data))

Generator写法

const fs = require('fs')
function getTxt (path) {
    return new Promise((resolve, reject) => {
        fs.readFile(path, 'utf-8', (err, data) => {
            if (err) reject(err)
            resolve(data)
        })
    })
}
function * fun () {
    yield getTxt('./a.txt')
}
const run = fun()
run.next().value.then(data => console.log(data))

async/await写法

const fs = require('fs')
function getTxt (path) {
    return new Promise((resolve, reject) => {
        fs.readFile(path, 'utf-8', (err, data) => {
            if (err) reject(err)
            resolve(data)
        })
    })
}
async function run (params) {
    const file = await getTxt(params)
    console.log(file)
    return file
}
run('./a.txt')