Node.js 基础入门

https://nodejs.org/zh-cn/download/

mkdir node
cd node
npm init -y

const { readFile } = require('fs')

readFile('./package.json', { encoding: 'utf-8' }, (err, data) => {
    if (err) {
        throw err;
    }
    console.log(data)
})

node index.js

// greeting.js
const prefix = 'hello';
const sayHi = function () {
    return prefix + 'world';
}
module.exports = {
    sayHi
}

// index.js
const { sayHi } = require('./greeting');
sayHi();

// greeting.js
const prefix = 'hello';
const sayHi = function () {
    return `${prefix}  world`;
}
exports.sayHi = sayHi;

// index.js
const { sayHi } = require('./greeting');
sayHi();

function (exports, require, module, __filename, __dirname) {
    const m = 1;
    module.exports.m = m;
}

// 有缓存
const mod1 = require('./foo');
const mod2 = require('./foo');
console.log(mod1 === mod2);     // true

//无缓存
function requireUncached(module) {
    delete require.cache[require.resolve(module)];
    return require(module);
}
const mod3 = requireUncached('./foo');
console.log(mod1 === mod3);     // false

var fs = require("fs") // 引入 fs 模块
fs.readFile(filename, [options], callback); //读取文件
fs.writeFile(filename, data, [options], callback); // 写文件
fs.appendFile(filename, data, [options], callback); //以追加的方式写文件
fs.open(filename, flags, [mode], callback); //打开文件
fs.mkdir(path, [mode], callback); //创建目录:
fs.readdir(path, callback); //读取目录
fs.exists(path, callback); //查看文件与目录是否存在

var path = require("path") // 引入 path 模块
path.basename(path[, ext]); //返回path的最后-部分
path.dirname(path); // 返回path的目录名
path.normalize(path);//路径解析,得到规范路径
path.isAbsolute(path); //判断路径是否是绝对路径
path.relative(form,to); //方法根据当前工作目录返回从from 到to的相对路径
path.resolve([...paths]); //将路径或路径片段的序列解析为绝对路径

var os = require("os") //引入 os 模块
os.cpus(); //返回每个逻辑cpu内核信息
os.hostname(); //返回操作系统的主机名
os.platform(); //返回标识操作系统平台的字符串
os.userInfo([options]); //返回关于当前有效用户的信息

const fs = require('fs')

fs.readFile('./package.json', { encoding: 'utf-8' }, (err, data) => {
    if (err) throw err;
    const { main } = JSON.parse(data);
    fs.readFile(main, { encoding: 'utf-8' }, (err, data) => {
        if (err) throw err;
        console.log(data)
    })
})

const { readFile } = require('fs/promises')

readFile('./package.json', { encoding: 'utf-8' }).then(res => {
    return JSON.parse(res);
}).then(data => {
    return readFile(data.main, { encoding: 'utf-8' });
}).then(res => {
    console.log(res);
})

function promisify(fn, receiver) {
    return (...args) => {
        return new Promise((resolve, reject) => {
            fn.apply(receiver, [...args, (err, res) => {
                return err ? reject(err) : resolve(res);
            }]);
        });
    };
}
const readFilePromise = promisify(fs.readFile, fs);

const { readFile } = require('fs/promises')

async () => {
    const { main } = JSON.parse(await readFile('./package.json', { encoding: 'utf-8' }));
    const data = await readFile(main, { encoding: 'utf-8' });
    console.log(data);
}

//发布订阅模式
const EventEmitter = require('events');

class MyEmitter extends EventEmitter { }
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
    console.log('an event occurred!');
});
myEmitter.emit('event');

// server 监听request 事件
const http = require('http');
const server = http.createServer((req, res) => {
	res.end('hello')
});
server.on('request', (req, res) => {
    console.log(req.url);
});
server.listen(3000);

const http = require('http');

http.createServer((req, res) => {
    res.end('hello World\n');
}).listen(3000, () => {
    console.log('App running at http://127.0.0.1:3000/')
})

const Koa = require('koa');
const app = new Koa();

app.use(async ctx => {
    ctx.body = 'Hello World';
});

app.listen(3000, () => {
    console.log('App running at http://127.0.0.1:3000/')
});