Express

website ：https://www.expressjs.com.cn/

Express Execution principle ： First find out whether there is a corresponding static resource , See if there are static resources , If there are static resources, execute static resources , If there are no static resources, find the route matching dynamic resources , Find dynamic resources , Execute dynamic resources , If not, execute 404.

middleware ： Middleware mainly refers to encapsulating all Http How to request details , It's from Http Processing method from request initiation to response end . Its biggest feature , It's a middleware processing , Pass it on to the next middleware .

Global installation

1. Install the generator to the global
   npm install -g express-generator

2. Create a new directory , And enter the directory from the command line

3. Execute the command to generate the project skeleton

   express

4. Execute the command to download all dependent packages

   npm install

5. Execute the command to start the server

   npm start

Partial installation

1. Create a new directory , And enter the directory from the command line

2. adopt npx Build project skeleton

   npx express-generator

3. Execute the command to download all dependent packages

   npm install

   abbreviation ：npm i

4. Execute the command to start the server

   npm start

Content introduction

package.json Run in

 "scripts": {
    
    "start": "node ./bin/www",   // If you want to start this, just npm startjiuxing 
    "hello": "node ./bin/www"	 // This is not start If you want to, you need to npm run hello Talent 
  },

If you want to change the port number , It's just bin Under the document www The following changes

var port = normalizePort(process.env.PORT || '3000');

route

For dynamic resources

Concept ：

build Web The server , One of the most basic functions is to deal with HTTP request , And return the correct content according to the request . For different HTTP request , We need to establish a way to deal with . This article will briefly introduce Express Routing Middleware in .

Parameters to obtain

1. request.params
2. request.query :get Submit the method to get parameters
3. request.body :post Submit the method to get parameters
4. res.send: Message return

Primary route

app.js Inside

// Primary route 
// Access level 1 routing ：http://localhost:3000/users
app.use('/', indexRouter);
app.use('/users', usersRouter);

Secondary route

routes Inside the folder

// Secondary route 
// Access the secondary route ：http://localhost:3000/users/reg
router.get('/', function(req, res, next) {
    
  res.send('respond with a resource');
});
router.get('/reg', function(req, res) {
    
  res.send('respond with a resource reg');
});

get and post The difference between

To obtain parameters : Use when you have a form post Submit , If there is no form, use get Submit

get:

1. Access is more direct and simple

2. There is a limit on the length of the requested road force , Different browsers have different restrictions

3. Parameters follow the path , Low security

4. Parameters are historical

How to get parameters

router.get('/reg', function(req, res) {
    
  let {
    username,pwd} = req.query;
  console.log(" User name and password ",username,pwd);
  res.send('get Submit successfully ');
});

post:

1. You must use a form or AJAX Initiate request

2. There is no limit on the length of paths and parameters

3. Parameters are placed in the request message body , Relatively high security

4. Parameter has no history

How to get parameters

 <form action="/users/login" method="post">
            <label for="username"> user name ：</label>
            <input type="text" name="username" id="username">
            <br>
            <label for="pwd"> password ：</label>
            <input type="text" name="pwd" id="pwd">
            <br>
            <input type="submit" value=" Submit ">
 </form>
 
 router.post('/login', function(req, res) {
    
  let {
    username,pwd} = req.body;
  console.log(" User name and password ：",username,pwd);
  res.send('post Submit successfully ');
 });
    

layered

effect

Responsibilities are clearer

Increase code flexibility and scalability

Improve maintainability

Three layer architecture

1. The presentation layer

Mainly accept requests from users , And data return , Provide access to applications for clients .

2. The business layer

Mainly responsible for the operation of data layer . That is to say, some data layer operations are combined .

3 Persistence layer

It mainly depends on whether the data layer contains logical processing , In fact, its functions mainly complete the operation of data files . Without any other operation .

MVC Three layer architecture

Only belong to the presentation layer

Pagination

1. effect

1. Improve rendering
2. Improve user experience

2. How to paginate

Front end paging

• ui Component sub packaged paging control

Back end paging

• Program code paging
  • advantage ： generality
  • shortcoming ： Memory consumption is too high , Performance degradation
• Database query paging ‘（ The main use of ）
  • advantage ： Low memory consumption , High performance
  • shortcoming ： Low versatility

3. The core concept

1. Page number
2. Number of displays per page
3. The total number of data
4. Total page number =Math.ceil( The total number of data / Number of displays per page )

db.getCollection("students").find({
    }).limit(5).skip(10);
// Page number minus 1* Display number 
//limit： Number of display bars  skip： Show the number of 

use ）

• advantage ： Low memory consumption , High performance
• shortcoming ： Low versatility

3. The core concept

1. Page number
2. Number of displays per page
3. The total number of data
4. Total page number =Math.ceil( The total number of data / Number of displays per page )

db.getCollection("students").find({
    }).limit(5).skip(10);
// Page number minus 1* Display number 
//limit： Number of display bars  skip： Show the number of