I am converting the old java code to node.js. First, I refer to this page, I used the prepared statement sample code. However, I found that the sample code quite clumpy, so I give up to use this code.

After that, I found the promise method, the example code is much simpler. So, I created a database class for accessing a MySQL Database.

class DBO
{
	constructor(){
		const mysql = require('mysql2');
		const dbConfig={
				charset	:"utf8",
				host		:"yourServer",
				user     	:"userName",
				password	:"password",
				port		:3306,
				database 	:"school"
			};
		dbConfig["multipleStatements"]=true;
		dbConfig["insecureAuth"]=true;	
		const connection = mysql.createConnection(dbConfig);

		/************************
                 * Get a student record *  
                 ************************/ 
                this.getStudent=async(stdId=>{
                   let sqlString ="select * from student where id=?"; 
                   return await executeQuery(sqlString,[stdId]);
                });

                /*******************************
                * Get a list of student record *
                ********************************/ 
                this.getStudentList=async(year, month)=>{
			let sqlString ="select * from student";
			return await executeQuery(sqlString);
		}
		this.close=()=>{
			connection.end(err=>{
				if (err) throw err;
				console.log("Disconnect from "+dbConfig["host"]+" successfully!");
			});
		}

                /************************************************************************
                 * Put the query code into a function for making the code more readable.*
                 ************************************************************************/ 
		function executeQuery(sql,para){
			return connection.promise().query(sql,para)
                        .then(([rows]) => {
				return rows
			})
                        .catch(err=>{                
                           throw(err);
                        })	
	       }			
    }
}

The following sample code is used to call the object directly.

let dboObj=new DBO();
dboObj.getStudentList()
.then(result=>{
	console.log("Get Student List ok");
})
.catch(err=>{
	console.log("Some wrong when getting data:"+err);
})
.finally(()=>{
	dboObj.close();
});

To call the DBO object from another object:

class Student
{
   constructor(stdId){
     this.id='';
     this.name='';
     this.class='';

     if (stdId!==undefined){
       let DBO=require("./dbo.js"); 
       let dboObj=new DBO();          

       dboObj.getStudent(stdId)
       .then(result=>{
         this.id=stdId;
         this.name=result.name; 
         this.class=result.class;
       })
       .catch(err=>{
          console.log("Some wrong when getting a student record:"+err);
       })
       .finally(()=>{
         dboObj.close();
       });
     }   
   }
   static async getStudentList(){
      let DBO=require("./dbo.js");
      let dboObj=new DBO();
      let resultObj={};

      try{
           let resultList=await dboObj.getStudentList(); 
           resultList.forEach(result=>{
               let studentObj=new Student();
               studentObj.name=result.name;
               studentObj.class=result.class;
               resultObj[result.id]=studentObj;
           });
           return resultObj;
      }
      catch(err){
	 throw(err);
      }
      finally{
	 dboObj.close();
      }
   }
}

#javascript

#mysql