nodeJS from entry to advanced

A, Node.js basics

1, the concept of

Simply put Node.js is running on the server side JavaScript.
Node.js is a JavaScript runtime environment
Node.js uses an event-driven, non-blocking I / O model, making it lightweight and efficient.

2, installation
Download the official website address: http: //nodejs.cn/

nodeJS5 basic objects:
1, require the introduction of module

2, export export target

grammar:

1）export.属性 = 值；
2）export.方法名 = 函数；

note:

1）export时module对象的引用 export == module.export （指向同一个内存空间）
2）export是module.export的引用， 不能改指向，只能添加属性和方法
3）module.export才是真正的暴露对象，指向哪里就暴露哪里-----推荐使用

3, module module object
module.export module.export.属性 = 值; module.export.方法名 = 函数； module.export = 对象或函数 module.id 模块id，模块名称 module.parent 模块父级 module.filename 模块文件名和路径 module.children 子模块列表 module.paths 模块查找路径，如果当前目录找不到node_modules就去上一级目录找，直到根目录
4, __ filename of the current absolute path js file
5, __ current js file folder absolute path where the file dirname

npm package manager (node Package Manager)
package.json is node.js project description file that describes the project as json format
Creating package.json file ----> npm init npm init -y ----> automatic creation of all yes
package.json common attributes
name: 项目名称 version:版本号 description:项目描述 main：主模块 dependencies：项目依赖 devDependencies ：开发时依赖 scripts:脚本命令，可以使用npm命令执行 license:开源协议
npm common commands:
npm install <包的名称> i--->install npm i <包的名称>@版本号 //安装指定版本 npm i <包的名称> -g全局安装 -S(save)写入项目依赖列表 -D(dev)写入开发依赖列表 npm search <包的名称> //搜索包 npm view <包的名称> //查看包 npm uninstall <包的名称> //卸载包 npm update <包的名称> //更新包

cnpm (Taobao Mirror)
asl install -g cnpm --registry = https: //registry.npm.taobao.org

nodeJS callback function
Callback mechanism:
- a., define a normal function
- b. The function passed as a parameter to another function (the caller)
- c. The caller decision based on the timing and conditions during execution if the calling function
The callback function uses:
- Usually used when the condition reaches a certain opportunity or need to execute code using a callback function

Synchronous and asynchronous

Synchronization: After the completion of the implementation of the previous line, the next line to be implemented
Asynchronous: the more complex tasks in order to achieve the task threads, without waiting for the completion of an execution, the next one can be executed.

Three kinds of asynchronous implementations:

(1) callback function
callback function is not necessarily asynchronous (forEacch), asynchronous callback function must have
(2) events (for server-side event)
event sources .on ( 'Event Name', the callback function)

/* 开启一个服务器*/
var http = require('http');
// 建立服务器
var app = http.createServer(function(request, response) {
    response.writeHead(200, {
        "Content-Type": "text/plain"   
    });
    response.end("Hello world!");
});
//启动服务器
app.listen(80,function(){
    console.log('服务器已运行')
})

(3) promise commitment Objects

/*
什么是promise?
    promise是es6中新增的承诺对象，用于对异步的操作进行消息的传递
promise的状态?
    Pending     等待中
    Resolved    成功
    Rejected    失败
    Pending => Resolved
    Pending => Rejected
promise 有什么用？
    promise可以传递异步消息
    由于异步的返回结果时间顺序不可控，所以需要使用promise来统一控制输出结果
*/
var promise = new Promise(function(resove,reject){
    resolve()
})
//调用对象
promise.then(res>{
    //成功的回调
}).catch(err=>{
    //失败的回调
})

//利用promise对象的all方法可以实现手动调整输出顺序，相当于把异步变为同步
Promise.all([p1,p2]).then(datas=>{
    //返回数组
})

Two, Buffer cache, and the file module

1, Buffer cache

concept

Opened up a staging area in memory for storing operation we need to bytecode

Create a buffer zone
Create a specified length buffer

var buf = new Buffer(大小) //创建5个字节的缓存区
buf.write('a') //存入一个字节  转成16进制 的Ascall码的61  在node中默认使用utf-8编码，一个中文3个字节

Create a buffer in the specified array coding

var buf = new Buffer([十进制编码]) //数字小可以

Create a character buffer specified

var buf = new Buffer('字符串')

Write buffer

buf.write('字符串')

Reading cache

buf.toString()

Copy buffer

buf.copy(buf2)

2, module file (fs)

Read the file

Since nodejs is the server program, you must have read and write files in the client does not have such a function
File read and write in two ways:
- Direct reading:
  - Everything on the hard disk only trigger callback function after all read into memory
  - Two way:
    异步：定义一个回调函数，接收读取到的内容 fs.readFile('文件路径',(err,data)=>{}) 同步：几乎所有fs的函数都有同步版本，只需在异步版本后面加Sync即可（Async：异步） fs.readFileSync('文件路径')
- Streaming read:
  - The data read from a hard disk triggers a callback function, to achieve a large file operations
    
    Write file
Synchronized version

fs.writeFileSync('文件名'，'数据')

Asynchronous version

fs.writeFile('文件名'，'数据'，funciton(err){/*写完文件以后执行的代码*/})

Reads the file information

fs.stat('文件名',function(err,state){
    //state时文件信息对象，包含了常用的文件信息
    //size： 文件大小，单位字节
    //mtime: 文件修改时间
    //birthtime 文件创建时间

    //方法
        .isFile() //判断当前查看的对象是不是一个文件
        .isDirectory() //判断是不是一个目录  
})

Delete Files

fs.unlink('文件名',function(err){})

Demand: Enter code implements delete a non-empty directory

Delete empty directories

fs.rmdir()

Read files in the directory and folder list

fs.readdir()

Read the details of each folder

fs.stat()

If it is judged file

fs.unlink()

If the judgment is a directory

//递归调用自己

Delete empty directories

fs.rmdir()

Stream reader

Flow: What is the flow
- All Internet data are streamed, a group of flow starting with a data transmission end

Flow of operation:

Streaming read the file

//可读取数据的流
var fs = require("fs");
var data = '';

// 创建可读流
var readerStream = fs.createReadStream('input.txt');

// 设置编码为 utf8。
readerStream.setEncoding('UTF8');

// 处理流事件 --> data, end, and error
readerStream.on('data', function(chunk) {
data += chunk;
});

readerStream.on('end',function(){
    console.log(data);
});

readerStream.on('error', function(err){
    console.log(err.stack);
});
console.log("程序执行完毕");

Streamed write file

//可写入数据的流
var fs = require("fs");
var data = 'hello world';

// 创建一个可以写入的流，写入到文件 output.txt 中
var writerStream = fs.createWriteStream('output.txt');

// 使用 utf8 编码写入数据
writerStream.write(data,'UTF8');

// 标记文件末尾
writerStream.end();

// 处理流事件 --> data, end, and error
writerStream.on('finish', function() {
    console.log("写入完成。");
});

writerStream.on('error', function(err){
    console.log(err.stack);
});

console.log("程序执行完毕");

Flow conduit
pipe provides a mechanism for outputting the input flow stream. We typically used to obtain the data from one data stream to another stream passing

`` `JavaScript
var FS = the require (" FS ");

// create a stream-readable
var readerStream = fs.createReadStream ( 'input.txt' );

// Create a writable stream
var writerStream = fs.createWriteStream ( 'output.txt' );

// write pipeline operation
// Read input.txt file content, and the content is written to a file output.txt
readerStream.pipe (writerStream);
console.log ( "program is finished");
`` `
Chain Flow

//压缩文件
var fs = require('fs');
var zlib = require('zlib');
// 压缩 input.txt 文件为 input.txt.gz
fs.createReadStream('input.txt')
    .pipe(zlib.createGzip())
    .pipe(fs.createWriteStream('input.txt.gz'))
console.log("文件压缩完成。");

//解压文件
var fs = require("fs");
var zlib = require('zlib');

// 解压 input.txt.gz 文件为 input.txt
fs.createReadStream('input.txt.gz')
.pipe(zlib.createGunzip())
.pipe(fs.createWriteStream('input.txt'));

console.log("文件解压完成。");

Third, the common web crawler module

1, common module

path module

Formatting path

path.nomalize(p)

Stitching path (a plurality of the strings together into a complete path)

/*使用path.jon拼接文件路径和 连接符 拼接优点
    1.自动帮我们添加路径分隔符（根据当前操作系统）
    2.自动改正错误的路径分隔符
*/
path.join(path1,path2)
let url = path.join(__dirname,path1); //常用

Part of the return path folder

path.dirname(p)

Part of the return path file (the file name and extension)

path.basename(p)

Returns the path to the file name suffix

path.extname(p)

Returns a string object path.

path.parse(path)

Return path strings, and parse the object from the opposite

path.format(path)

url module

What is the url?
- url is the world's Uniform Resource Locator, a kind of website resources concise expression, referred to as URLs
url composition
- Complete
  protocol: // username: password @ hostname domain name: port number / directory / file name extension parameter name = value & parameter parameter name = parameter value 2 2 # hash.?
- Common
  protocol: // hostname domain name / directory / file name extension parameter name = value & parameter parameter name = parameter value 2 2 # hash.?
  
  2, the web crawler
  
  Fourth, the network server
  
  Five, express frame
  
  Six, Mongodb database
  
  Seven, mongoose operation database

nodeJS from entry to advanced

A, Node.js basics

1, the concept of

2, installation

nodeJS5 basic objects:

npm package manager (node ​​Package Manager)

cnpm (Taobao Mirror)

nodeJS callback function

Synchronous and asynchronous

Two, Buffer cache, and the file module

1, Buffer cache

concept

Create a buffer zone

Write buffer

Reading cache

Copy buffer

2, module file (fs)

Read the file

Write file

Reads the file information

Delete Files

Demand: Enter code implements delete a non-empty directory

Stream reader

Third, the common web crawler module

1, common module

path module

url module

2, the web crawler

Fourth, the network server

Five, express frame

Six, Mongodb database

Seven, mongoose operation database

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npm package manager (node Package Manager)