使用Node.js搭建一个简单的web服务器(一):Node.js入门

什么是Node

  1. 一个允许我们在计算机/服务器上运行JavaScript的平台
  2. 可以读取,删除和更新文件
  3. 可轻松的与数据库通信

优势

  • 使用JavaScript语言
  • 非常快(在V8引擎上运行并使用非阻塞代码)
  • 庞大的开源插件包生态系统 (npm)
  • 适合实时服务(如聊天)

下载Node.js

https://nodejs.org/
(左侧为目前稳定版本,右侧为最新版本)
使用Node.js搭建一个简单的web服务器(一):Node.js入门

创建&引入模块(module)

基本使用

在count.js文件下编写需要用到的module,并在app.js引入并使用。

//count.js
const counter = (arr) => {
  return `there are ${arr.length} elements in this array`;
};

module.exports = counter;
//必须export你想在其他文件使用的东西

//app.js
const counter = require(‘./count‘);
//counter==从count文件抛出的东西
console.log(counter([‘shuan‘, ‘cry‘, ‘ryu‘]));

当一个文件中需要抛出多个东西

module文件的写法

写法一:

//stuff.js
const counter = function (arr) {
  return `there are ${arr.length} elements in this array`;
};

const adder = function(a, b) {
  return `the sum of the two numbers is ${a + b}`;
}

let pi = 3.142;

module.exports.counter = counter;
module.exports.adder = adder;
module.exports.pi = pi;

写法二:

//stuff.js
const counter = function (arr) {
  return `there are ${arr.length} elements in this array`;
};

const adder = function(a, b) {
  return `the sum of the two numbers is ${a + b}`;
}

let pi = 3.142;
 module.exports = {
   counter: counter,
   adder: adder,
   pi: pi
 }

写法三:

//stuff.js
module.exports.counter = function (arr) {
  return `there are ${arr.length} elements in this array`;
};

module.exports.adder = function (a, b) {
  return `the sum of the two numbers is ${a + b}`;
}

module.exports.pi = 3.142;

app.js文件的写法

写法一:

//app.js
const {counter, adder, pi} = require(‘./stuff‘);

console.log(counter([‘shuan‘, ‘cry‘, ‘ryu‘]));
console.log(adder(5, 6));
console.log(adder(pi, 5));

写法二:

const stuff = require(‘./stuff‘);

console.log(stuff.counter([‘shuan‘, ‘cry‘, ‘ryu‘]));
console.log(stuff.adder(5, 6));
console.log(stuff.adder(stuff.pi, 5));

事件触发器

基本用法

//basic
const events = require(‘events‘);//导入Node的events模块

var myEmitter = new events.EventEmitter();//创建一个事件触发器对象

myEmitter.on(‘someEvent‘, (mssg) => {//注册监听器,给名为someEvent的事件的监听器数组末尾添加监听器(即该方法)
  console.log(mssg);

});

myEmitter.emit(‘someEvent‘, ‘the event was emitted‘);//触发someEvent事件的监听器,并传入参数

多个同类型的对象绑定事件触发器

方法一:

const events = require(‘events‘);
class Person extends events.EventEmitter {//让Person继承events.EventEmitter的特性
  this.name = name;
}
const james = new Person(‘james‘);
const mary = new Person(‘mary‘);
const ryu = new Person(‘ryu‘);
const people = [james, mary, ryu];

people.forEach((person) => {//使用forEach为每个Person对象注册监听器
  person.on(‘speak‘, (mssg) => {
    console.log(`${person.name} said: ${mssg}`);
  });
});

james.emit(‘speak‘, ‘hey dudes‘); 
ryu.emit(‘speak‘, ‘i want a curry‘)

方法二:

const events = require(‘events‘);
const util = require(‘util‘);
const Person = (name) => {
  this.name = name;
};
util.inherits(Person, events.EventEmitter); 
// 使用util.inherits(constructor, superConstructor) 实现继承 constructor.super_=superConstructor

const james = new Person(‘james‘);
const mary = new Person(‘mary‘);
const ryu = new Person(‘ryu‘);
const people = [james, mary, ryu];

people.forEach((person) => {
  person.on(‘speak‘, (mssg) => {
    console.log(`${person.name} said: ${mssg}`);
  });
});

james.emit(‘speak‘, ‘hey dudes‘); 
ryu.emit(‘speak‘, ‘i want a curry‘);

两种继承方法语义上不兼容,建议使用第一种方法

读写文件

同步&异步

  1. 同步读写文件(Sync):文件读写完前不会执行下面的代码
  2. 异步读写文件:传入回调函数后继续执行后续代码
//read file
const fs = require(‘fs‘);
const readMe = fs.readFileSync(‘readMe.txt‘, ‘utf8‘);//同步读取

fs.readFile(‘readMe.txt‘, ‘utf8‘, (err, data) => {
  fs.writeFile(‘writeMe.txt‘, data, (err) => {});
});//异步读取
console.log(‘test‘);
//test 会在fs.writeFile执行完之前打印

写文件

若同一文件目录下不存在‘writeMe.txt’,则创建新文件并写入数据,若存在则将文件内容替换成写入数据。写入数据必须为字符串或buffer二进制数据。

fs.writeFileSync(‘writeMe.txt‘, readMe);
fs.writeFile(‘writeMe.txt‘, data, (err) => {});

创建或删除目录

const fs = require(‘fs‘);
//删除文件
fs.unlink(‘writeMe.txt‘, (err) => {}); 

//创建 or 移除目录
fs.mkdirSync(‘stuff‘);
fs.rmdirSync(‘stuff‘);

fs.mkdir(‘stuff‘, () => {
  fs.readFile(‘readMe.txt‘, ‘utf8‘, (err, data) => {
    fs.writeFile(‘./stuff/writeMe.txt‘, data, (err) => {})
  })
})

fs.unlink(‘./stuff/writeMe.txt‘, () => {})
fs.rmdir(‘stuff‘, () => {})//必须是空文件夹

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