nodejs异步案例

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
over1
over2
over3
hello node dkplus!4
over4
hello node dkplus!1
hello node dkplus!3
hello node dkplus!2
------------------------*/