Express request methods -- get, post, patch, delete

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mention node I'll think of express, Just started learning express It's still a little difficult , stay b I've been looking for a lot of courses to see , Learn from the basics step by step .

Express

One 、 Introduce Express

Express Have a rich foundation API Support , And common HTTP Auxiliary program , For example, redirection 、 Cache, etc ; It has powerful routing function 、 Flexible middleware ; High performance and stability ;Express Only... Is provided web Basic functions of development , It passes through middleware The method integrates many external plug-ins to handle HTTP request .

• body-parser： analysis HTTP Request body
• compression： Compress HTTP Respond to
• cookie-parser： analysis cookie data
• cors： Handle cross domain resource requests
• morgan：HTTP Request logging
• ...

Express Middleware for Express Itself becomes more flexible and simple , The disadvantage is that although some middleware packages solve almost all problems or requirements across domains , But choosing the right package can sometimes be a challenge .Express incorrect Node.js Second abstraction of existing features , Just expand on it web The basic functions required by the application ;

• Internal use is still HTTP modular
• The request object inherits from ：http.IncomingMessage
• The response object inherits from ：http.ServerResponse

There are many popular frameworks based on Express, such as LoopBack、Sails、NextJs

Express Of Hello World

introduce express modular , Create a server , And then on the browser get Request to respond ;

const express = require('express');
const app = express();
app.get('/', (req, res) => {
    res.send('Hello World!');  //  Send a response 
})
app.listen(3000);
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Two 、 Routing basis

Routing is to determine how an application responds to a client's request for a particular endpoint , The specific endpoint is URI( Or the path ) And specific HTTP Request method (get,post etc. ). Each route can have one or more handler functions , These functions execute when matching the route ; Adopt the following structure to realize ：( As above get request )

app.method(path, handle); 
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• app yes Express example
• method It's lowercase HTTP Request method
• path It's the path on the server
• handle Is the function performed when the route matches

Requests and responses

Express The application uses the parameters of the route callback function ：request and response Object to process the corresponding request and response data ;

• Request object ： Get information about the request ; Inherited from http.IncomingMessage

• stay express Through req.query Get request parameters ; Specific reference Express - API file

• The response object ： Used to process requests and send responses ; Inherited from http.ServerResponse

  res.cookie('foo', 'bar');
  res.status(201).send({foo: 'bar'});    //  Set the status and respond 
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3、 ... and 、 Four ways to request

When we write each route , Generally, you have to read some content and respond to the browser , For example, we put the data in db.json In the document , And then again app.js Used in documents fs.readFile() Reading data ; Here we can put app.js Some frequently used methods used in are written in another file db.js Inside , such as fs.readFiles() Method ;

const fs = require('fs')
const { promisify } = require('util')
const path = require('path');
const readFile = promisify(fs.readFile);
const dbPath = path.join(__dirname, './db.json');  //  Absolute path 
exports.getDb = async () => {
    const data = await readFile(dbPath, 'utf-8');
    return JSON.parse(data);
}
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1. get request

After encapsulation, in app.js Pass through await getDb() You can get the corresponding data content ;( Remember async); If it doesn't exist, go back 404 Status code , If found, respond to the found data content ; use try...catch To avoid a small number of errors that make the whole program unable to run ; Be careful ：req.params For request parameters

const { getDb } = require('./db')
app.get('/todos/:id', async (req, res) => {
    try {
        const db = await getDb();
        const todo = db.todos.find(todo => todo.id === Number.parseInt(req.params.id));
        if (!todo) { return res.status(404).end(); }
        res.status(200).json(todo);
    } catch (err) {
        res.status(500).json({
            error: err.message
        })
    }
})
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2. post request

• Configure parsing form request body

  application/json：app.use(express.json()); take json Data in the form of js object ;

  application/x-www-form-urlencoded：app.use(express.urlencoded)

• post We usually use it to submit data , Here we need to use fs.writeFile;

• similarly , Write the method in db.js In file ; When writing data , If we want to make json If the data in appears to be formatted , With (db, null, ' ') Is a parameter ;

  exports.saveDb = async () => {
      const data = JSON.stringify(db, null, ' ');  //  Give Way db.json The data in has a format 
      await writeFile(dbPath, data);
  }
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• Later on app.js Process the data , If todo.title If it doesn't exist, go back 404, If it exists, the data will be added push To the corresponding array (todo) in , Write data after data submission ;

  try {
      if (!todo.title) {
          return res.status(404).json({ error: 'The field title is required' })
      }
      const db = await getDb();
      const lastTodo = db.todos[db.todos.length - 1];
      todo.id = lastTodo ? lastTodo.id + 1 : 1;
      db.todos.push(todo);
      await saveDb(db);
      res.status(200).json(todo);
  } catch (err) {
      res.status(500).json({
          error: err.message
      })
  }
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3. patch request

• First pass req.body Get form data ：const todo = req.body;

• Find the task item to modify , If you don't find it, you don't have to change it , Go straight back to 404 that will do ; If found, modify the data ,

  const db = await getDb();
  const ret = db.todos.find(todo => todo.id === Number.parseInt(req.params.id));
  if (!res) {
      return res.status(404).end();
  }
  Object.assign(ret, todo);
  await saveDb(db);
  res.status(200).json(ret);
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  Be careful ：Object.assign The method is shallow copy , The first parameter is the target object , Later parameters are all source objects ; If the target object has the same property as the source object , Or multiple source objects have properties with the same name , Then the following properties will overwrite the previous properties ;

4. delete operation

• Find the item to delete

  const todoId = Number.parseInt(req.params.id);
  const db = await getDb();
  const index = db.todos.findIndex(todo => todo.id === todoId);
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• findIndex This API Find return index , If you don't find it, go back -1; Once found, delete this data ;

  if (index === -1) { return res.status(404).end(); }
  db.todos.splice(index, 1);
  await saveDb(db);
  res.status(200).end();
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I've always been curious about how the browser and server connect , Finally learned express Understand the process