const fs = require('fs');fs.readFile('./test.txt', 'utf-8', (err, data) => { ?err ?? console.error(err) ?: console.log(data.toString()+'1');});console.log("over1");fs.readFile('./test.txt', 'utf-8', (err, data) => { ?setTimeout(() => { ???err ???? console.error(err) ???: console.log(data.toString()+'2'); ?}, 100);});console.log("over2");fs.readFile('./test.txt', 'utf-8', (err, data) => { ?err ?? console.error(err) ?: console.log(data.toString()+'3');});console.log("over3");var data = fs.readFileSync('./test.txt');console.log(data.toString()+'4');console.log("over4");/*------------------------输出结果如下over1over2over3hello node dkplus!4over4hello node dkplus!1hello node dkplus!3hello node dkplus!2------------------------*/nodejs异步案例
原文地址：https://www.cnblogs.com/dkplus/p/8447789.html