Connection pool and how it works?

Question

JavaScript

Hello to all!
There is a code:

const mysql = require("mysql2");
const pool = mysql.createPool({
    host: "localhost",
    user: "use",
    database: "dadb",
    password: "pass"
   }).promise();
const sql = 'SELECT secret FROM validation_table WHERE name=?;'
const name = 'flowerr'
pool.query(sql,name)
.then(result =>{
    let res = result[0]
    console.log('result = ',res[0]);
    pool.end();
})
.then(() =>{
  console.log("end"); 
})
.catch(function(err) {
  console.log(err.message);
})

result in console:

result =  undefined
end

How to break the script on the first ".then" if the received value = "undefined"?
Thank you!

Answer 1

.then(result =>{
    let res = result[0]
    console.log('result = ',res[0]);
    pool.end();
if( result === undefined ) throw new Error();
})
.then(() =>{
  console.log("end"); 
})
.catch(function(err) {
  console.log(err.message);
})

if you throw your error, then the next then will be skipped, and the error will be caught in catch