Javascript 之 async 四重奏（一）

fs.readdir(source, function (err, files) { if (err) {   console.log('Error finding files: ' + err) } else {   files.forEach(function (filename, fileIndex) {     console.log(filename)     gm(source + filename).size(function (err, values) {       if (err) {         console.log('Error identifying file size: ' + err)       } else {         console.log(filename + ' : ' + values)         aspect = (values.width / values.height)         widths.forEach(function (width, widthIndex) {           height = Math.round(width / aspect)           console.log('resizing ' + filename + 'to ' + height + 'x' + height)           this.resize(width, height).write(dest + 'w' + width + '_' + filename, function(err) {             if (err) console.log('Error writing file: ' + err)           })         }.bind(this))       }     })   }) }})

function getData(count) {   get(`/sampleget?count=${count}`, data => {       console.log(data);   });}
function queryDB(kw) {   db.find(`select * from sample where kw = ${kw}`, (err, res) => {       getData(res.length);   });}
function readFile(filepath) {   fs.readFile(filepath, 'utf-8', (err, content) => {       let keyword = content.substring(0, 5);       queryDB(keyword);   });}readFile('./sample.txt');