preface

Preparation before starting:

• 1, install mysql; Write a code for the login and registration page.
• Create your own database (myFirst) and table (user);
• 3. Encapsulate the SQL statement operation module;
• 4. Install express module;

Knowledge reserves

• 1. Node is modular
• 2. Database connection pooling and encapsulation
• 3. How callback functions work
• 4. Expres module

Requirements and Principles

landing

We’re going to implement the user to enter a username and password in the input box, and then we’re going to match the user’s input to the information in our database and if it’s there it’s a login success or it’s a login failure. (Note: we are not making regular judgments about the content in the input box.)

registered

The user input the account and password, we will submit the account and password entered by the user to save to our database, save the successful registration is successful, otherwise it is failure. (Note: we are not making regular judgments about the content in the input box.)

The principle of

• 1. To obtain the operation of the database, we need to download the data module in Node, and then encapsulate the operation of the database SQL statement, which is convenient for our subsequent use.
• 2. We also need to create a service. The data submitted by the form is checked against our database through the service’s request and feedback.
• We use the Express module to create the service (instead of using the built-in HTTP module of Node.js).

Database whitelist

Note: when we register successfully, a data entry will be added to the table

Encapsulate SQL statement operations

const mysql = require("mysql");
/ / the connection pool
const pool = mysql.createPool({
  host:"localhost".user:"root".// The account name of my local database
  password:"123456".// My local database login password
  database:"myfirst".// The name of the database I created myself
  / / is optional
  queueLimit:3.connectionLimit:20
})
// Add a query method
let query = function(sql,callBack){
  pool.getConnection((err,conn) = >{
    if (err) {
      console.log(err);
      return
    }
    conn.query(sql,(err,data) = >{
      if (err) {
        console.log(err);
        return
      }
      if(callBack) { callBack(data); }})})}/** * Insert data *@param {*} Table table name *@param {*} Datas data object *@param {*} CallBack callBack function */ after successful insertion
let insert = (table,datas,callBack) = >{
  / / stitching SQL
  let fields = ' ';/ / field
  let values = ' ';/ / value
  for (const k in datas) {
    fields += k+"," // Concatenate fields
    values += ` '${datas[k]}', `
  }
  // Clear the last comma.
  fields = fields.slice(0, -1);
  values = values.slice(0, -1);
  // console.log(fields);
  // console.log(values);
  let sql = `INSERT INTO ${table} (${fields}) VALUES (${values}) `;
  query(sql,callBack)
};

// Encapsulate a delete SQL method
let del = (table,datas,callBack) = >{
  let arr = ['1 = 1']; // Avoid exception error when datas is empty.
  for (const k in datas) {
    arr.push(`${k} = '${datas[k]}'`);
  }
  let sql = `delete from ${table} where ${arr.join(" and ")}`;
  query(sql,callBack)
}
/** * Modify method *@param {string} Table table name *@param {object} Sets Indicates the field and value *@param {object} Wheres' judgment condition *@param {Function} CallBack function */
let update = (table,sets,wheres,callBack) = >{
  // Prepare an array to concatenate the WHERE clause
  let whereArr = ['1 = 1']; // Avoid exception error when datas is empty.
  for (const k in wheres) {
    whereArr.push(`${k} = '${wheres[k]}'`);
  }
  // Prepare an array to concatenate the set clause
  let setArr = [];
  for (const k in sets) {
    setArr.push(`${k} = '${sets[k]}'`)}let sql = `UPDATE ${table} SET ${setArr.join(",")}  WHERE ${whereArr.join(" and ")}`
  query(sql,callBack)
}
/ / export
module.exports = {
  query,
  insert,
  del,
  update
};

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Note: How to initialize mysql and how to download mysql and how to operate mysql

Create a service

app.jsfile

const express = require('express')
// Create a service
const app = express()
const port = 3001
// Import the routing module
app.use(require("./login"));
// This is the server port number
app.listen(port, () = > console.log(`Example app listening on port ${port}! `))
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Data acquisition and processing

The login. Js file

const express = require('express')
// Introduce encapsulated SQL statement manipulation module
const db = require('./db')
// Call the express.rotuer () method to create a routing object
const login = express.Router();
// The post parameter is parsed. Write it before the route
login.use(express.urlencoded({ extended: false }));
// Mount the specific route on the route object.


/ / login
login.post('/login'.(req, res) = > {
  let { username, pwd } = req.body;
  // Call the encapsulated query to check whether the data is identical. If the data is identical, the callback data returns a non-empty array
  db.query(`select * from user where name = '${username}' and pwd = '${pwd}'`.(data) = > {
    if (data.length > 0) {
      res.send('Login successful')}else {
      res.send('Login failed')}})})/ / register
login.post('/register'.(req, res) = > {
  // Destruct the assignment
  let { username:name, pwd:pwd } = req.body;
  db.insert('user', { name,pwd }, (data) = > {
    if (data.affectedRows > 0) {
      res.send("Registration successful!")}else {
      res.send("Registration failed!")}})})// Export the routing object with module.exprots
module.exports = login;
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HTML part

  <! -- login -- style yourself!! -->
  <form action="http://127.0.0.1:3001/login" method="post">User name:<input type="text" name="username"><br>Password:<input type="password" name="pwd"><br>
    <input type="submit" value="Login" id="btn">
  </form>
  <! -- Registration -- style your own!! -->
  <form action="http://127.0.0.1:3001/register" method="post">User name:<input type="text" name="username"><br>Password:<input type="password" name="pwd"><br>
    <input type="submit" value="Registered" id="btn">
  </form>
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The effect