06. First introduction to express

1、 What is? Express

【 explain 】： Express Is based on Node.js platform , Fast 、 to open up 、 minimalist Web Development framework .

【 The essence 】： It's just one. npm Third party packages on , Provides a quick way to create Web A convenient way for servers

【 Chinese official website 】： https://www.expressjs.com.cn/

2、Express The role of

• For front-end programmers , The two most common servers , Namely ：
• Web Web server ： Specialized in providing Web Web resource server .
• API Interface server ： Specialized in providing API Interface server .

3、Express Basic use of

1、 install Express

In the directory where the project is located , Run the following terminal command , Can be express Install into the project to use ：

npm i [email protected]4.17.1  

2、 Create basic web The server

//  Import express
const express = require('express')

//  establish web The server 
const app = express();

//  Start the server 
app.listen(80, () => {
    
    console.log('express running at http://127.0.0.1');
})

3、 monitor GET request

【 explain 】： adopt app.get Can listen to the user's get request The specific syntax is as follows

// Parameters 1: Represents the address requested by the client 
// Parameters 2： Requested handler 
// req: Request object 
// res： The response object 
app.get('url',(req,res)=>{
    } /* Processing function */)

【 Code example 】：

//  Import express
const express = require('express')

//  establish web The server 
const app = express();

//  Listen to the client get request 
app.get('/user', (req, res) => {
    
    //  call res.send() Method to respond to a client json object 
    res.send({
    
        name: ' Zhang San ',
        age: 20,
        gender: ' male '
    })
})
//  Start the server 
app.listen(80, () => {
    
    console.log('express running at http://127.0.0.1');
})

4、 monitor POST request

【 explain 】： adopt app.post Can listen to the user's get request The specific syntax is as follows

// Parameters 1: Represents the address requested by the client 
// Parameters 2： Requested handler 
// req: Request object 
// res： The response object 
app.post('url',(req,res)=>{
    } /* Processing function */)

【 Code example 】：

//  Import express
const express = require('express')

//  establish web The server 
const app = express();

//  Listen to the client post request 
app.post('/user', (req, res) => {
    
    //  call res.send() Respond to a string 
    res.send(' The request is successful ！！')
})
//  Start the server 
app.listen(80, () => {
    
    console.log('express running at http://127.0.0.1');
})

5、 The response content is sent to the client

【 explain 】： adopt res.send() Method , You can put the processed content , Send to client ：

【 Code example 】：

//  Import express
const express = require('express')

//  establish web The server 
const app = express();

//  Listen to the client get request 
app.get('/user', (req, res) => {
    
    //  call res.send() Method to respond to a client json object 
    res.send({
    
        name: ' Zhang San ',
        age: 20,
        gender: ' male '
    })
})

app.post('user',(req,res)=>{
    
	res.send(' The request is successful ！！！')
})

//  Start the server 
app.listen(80, () => {
    
    console.log('express running at http://127.0.0.1');
})

6、 Get query URL Query parameters in

【 explain 】： adopt req.query object , You can access the client in the form of a query string , Parameters sent to the server

【 Code example 】：

//  Import express
const express = require('express')

//  establish web The server 
const app = express();

//  Get two url Parameters carried in 
//  adopt req.query You can get the passed parameters 
//  By default, it's an empty object 
app.get('/', (req, res) => {
    
	// Client side usage ?name=as&age=20 The parameters sent to the server can be sent through req.query Object access to 
    console.log(req.query);
    res.send(req.query)
})

//  Start the server 
app.listen(80, () => {
    
    console.log('express running at http://127.0.0.1');
})

7、 obtain URL Dynamic parameters in

【 explain 】： Can pass req.params object , visit url in , adopt ： Matching dynamic parameters ：

【 Code example 】：

//  Import express
const express = require('express')

//  establish web The server 
const app = express();
//  Get dynamic parameters 
//  Default req.params Is an empty object 
app.get('/user/:id',(req,res)=>{
    
	console.log(req.params)
	res.send(req.params)
})
//  Start the server 
app.listen(80, () => {
    
    console.log('express running at http://127.0.0.1');
})

8、 Hosting static resources

1、express.static()

【 explain 】： express Provides a very useful function , be called express.static(), Through it , We can easily create a static resource server .

【 Use the syntax 】：

app.use(express.static('public'))

【 explain 】：

• You can visit public All the files in the directory ：
• Express Find the file in the specified static Directory , And provide access path to resources . therefore , The directory name where the static file is stored will not appear in URL in

2、 Hosting multiple static resource directories

【 grammar 】：

app.use(express.static('public'))
app.use(express.static('files'))

【 explain 】：

• Call it many times
• Use the method of sequential search to find

3、 Mount path prefix

【 explain 】： If you want to be ahead of the managed static resource access path , Mount path prefix , You can use the following method ：

app.use('/public' ,express.static('public'))

9、nodemon

【 brief introduction 】： Writing debugging Node.js When the project is , If you change the project code , It requires frequent manual close fall , Then restart , Is cumbersome . Now? , We can use nodemon This tool , It can monitor changes in project files , When the code is modified ,nodemon Will automatically help us restart the project , It is very convenient for development and debugging

1、 install

npm i nodemon --save

2、 Use nodemon

nodemon app.js