通过程序来介绍 Node.js 的几个文件读写和事件监听 API

//导入模块const fs = require("fs"); const fileName = "foo.txt";//判断文件或文件夹是否存在fs.exists(fileName, (exists) => {    if (exists) {        //如果存在，查看文件或文件夹的属性        fs.stat(fileName, (error, stats) => {            if (error) {                throw error;            }            //如果是文件就读取文件            if (stats.isFile()) {                fs.readFile(fileName, "utf8", (error, data) => {                    if (error) {                        throw error;                    }                     console.log(data);                })                            }                   })    }})

const fs = require('fs')const path = require('path')fs.readFile(path.join(__dirname, '/data/customers.csv'), {  encoding: 'utf-8'},(err, data) = >{  if (err) {    console.error(err) process.exit(1)  } else {    console.log(data)  }
})

const fs = require('fs')fs.writeFile('message.txt', 'Hello World!', (err) = >{  if (err) {    console.error(err) process.exit(1)  } else {    console.log('Writing is done.')
  }})

const events = require("events");const emitter = new events.EventEmitter();const username = "colin";const password = "password";// an event listeneremitter.on("userAdded", (username, password) = >{  console.log("Added user " + username);});// add the user// then emit an event emitter.emit("userAdded", username, password);