Node.js【简介、安装、运行 Node.js 脚本、事件循环、ES6 作业队列、Buffer(缓冲区)、Stream(流)】(一)-全面详解（学习总结---从入门到深化）

node -v //查看nodejs版本
npm -v //查看npm版本

const bar = () => console.log('bar')
const baz = () => console.log('baz')
const foo = () => {
 console.log('foo')
 bar()
 baz()
}
foo()
//foo
//bar
//baz

const bar = () => console.log('bar')
const baz = () => console.log('baz')
const foo = () => {
        console.log('foo')
        setTimeout(bar, 0)
        baz()
}
foo()
//foo
//baz
//bar

const bar = () => console.log('bar')
const baz = () => console.log('baz')
const foo = () => {
 console.log('foo')
 setTimeout(bar, 0)
 new Promise((resolve, reject) =>
  resolve('应该在 baz 之后、bar 之前')
).then(resolve => console.log(resolve))
 baz()
}
foo()
//foo
//baz
//应该在 baz 之后、bar 之前
//bar

const bar = () => console.log('bar')
const baz = () => console.log('baz')
const foo = () => {
 console.log('foo')
 new Promise((resolve, reject) =>
 resolve('应该在 bar之后')
).then(resolve => console.log(resolve))
 process.nextTick(bar)
 baz()
}
foo()
//foo
//baz
//bar
//应该在 bar之后

// 引入 events 事件模块
var events = require('events');
// 创建 eventEmitter 对象
var eventEmitter = new events.EventEmitter();

eventEmitter.on('some_event', function(e)
{
  console.log('some_event 事件触发');
  console.log(e);
});

eventEmitter.emit('some_event','params')

eventEmitter.removeAllListeners([event])

const buf = Buffer.from('tong');

console.log(buf.toString())
console.log(buf.toString('utf-8',0,2))

const buf1 = Buffer.from('小童');
const buf2 = Buffer.from('程序员');
const buf3=Buffer.concat([buf1,buf2])
console.log(buf3.toString())
//console.log(buf1+buf2)

var fs = require("fs");
fs.readFile(__dirname + '/input.txt', (err, data) => {
  console.log(data.toString())
})

//可读流可以从一文件中读取信息。
//读取的数据可以暂时存放在缓存（Buffer）里，防止应用程序无法及时处理。
//创建可读流
var readerStream = fs.createReadStream('input.txt');
// 处理流事件
readerStream.on('data', function(chunk) {
  data += chunk;
});

const Stream = require('stream')
//首先创建流对象
const readableStream = new Stream.Readable()
//实现 readable._read() 方法
readableStream._read=()=>{}
//监听可读流里面是否有可读的数据
readableStream.on('data',(chunk)=>{
  console.log(chunk.toString())
})
//发送数据
readableStream.push('小童')
readableStream.push('程序员')

//创建可写流对象
const Stream = require('stream')
const writableStream = new Stream.Writable()
//实现_write
writableStream._write = (chunk, encoding, next) => {
 console.log(chunk.toString())
 next()
}
//写入数据
writableStream.write('hellow')
writableStream.write('world')

//可写流可以将数据写入文件中。
//为了防止因为写入目标处理速度太慢导致数据丢失，写入的数据可以暂存在可写流
//内部的缓存（Buffer）中。
//创建文件可写流对象
const fs=require('fs')
const writableStream =fs.createWriteStream('output.txt');
// 使用 utf8 编码写入数据
writableStream.write('hello','UTF8');
writableStream.write('xiaotong','UTF8');
// 标记文件末尾
writableStream.end();
// 监听写入文件完成
writableStream.on('finish', function() {
  console.log("写入完成。");
})