What does the && operator do?

The && or Logical AND operator finds the first falsy expression in its operands and returns it and if it does not find any falsy expression it returns the last expression. It employs short-circuiting to prevent unnecessary work. I've used this in the catch block when closing database connection in one of my projects.

   console.log(false && 1 && []); //logs false
   console.log(" " && true && 5); //logs 5

Using if statements.

  const router: Router = Router();

  router.get('/endpoint', (req: Request, res: Response) => {
     let conMobile: PoolConnection;
     try {
        //do some db operations
     } catch (e) {
     if (conMobile) {
      conMobile.release();
     }
  }
});

Using && operator.

const router: Router = Router();

router.get('/endpoint', (req: Request, res: Response) => {
  let conMobile: PoolConnection;
  try {
     //do some db operations
  } catch (e) {
    conMobile && conMobile.release()
  }
});