nodejs express中間部品の非同期フィードバック、koa中間部品のasync awaitの未来動向

async await        

const fs = require('fs') //nodejs      
const path = require('path') //nodejs      

// callback            
function getFileContent(fileName, callback) {
    const fullFileName = path.resolve(__dirname, 'files', fileName)  
    // __dirname     
    fs.readFile(fullFileName, (err, data) => {
        if (err) {
            console.error(err)
            return
        }
        callback(
            JSON.parse(data.toString())
        )
    })
}

//    callback-hell      
getFileContent('a.json', aData => {
    console.log('a data', aData)
    getFileContent(aData.next, bData => {
        console.log('b data', bData)
        getFileContent(bData.next, cData => {
            console.log('c data', cData)
        })
    })
})

//   promise       
function getFileContent(fileName) {
    const promise = new Promise((resolve, reject) => {
        const fullFileName = path.resolve(__dirname, 'files', fileName)
        fs.readFile(fullFileName, (err, data) => {
            if (err) {
                reject(err)
                return
            }
            resolve(
                JSON.parse(data.toString())
            )
        })
    })
    return promise
}

//  promise     

getFileContent('a.json').then(aData => {
    console.log('a data', aData)
    return getFileContent(aData.next)
}).then(bData => {
    console.log('b data', bData)
    return getFileContent(bData.next)
}).then(cData => {
    console.log('c data', cData)
})

async function readFileData() {
    //     
    try {
        const aData = await getFileContent('a.json')
        console.log('a data', aData)
        const bData = await getFileContent(aData.next)
        console.log('b data', bData)
        const cData = await getFileContent(bData.next)
        console.log('c data', cData)
    } catch (err) {
        console.error(err)
    }
}

readFileData()

async function readAData() {
    const aData = await getFileContent('a.json')
    return aData
}
async function test() {
    const aData = await readAData()  //            promise
    console.log(aData)
}
test()