Getting Timeout while inserting in transaction using node-mssql package sqlserver - sql

Question

I recently started using mssql package in my Node-Express Application for accessing the DB.
I read through various documents, including the implementation and tutorial on how to establish and use a connection. Here are the few things that I am confused upon.
Clarification
Is it a good practice to keep a connection open across the application, i.e. I have my current implementation like this.
global.sql = await mssql.connect(config, function (err) { /*LOGS*/});
And wherever, I query, I query like
function getItems(){
await sql.query`select * from tbl where val in (${values})
}
Is it the right way of doing things, or should I do it like this?
function getItems(){
const sql = mssql.connect()
await sql.query`select * from tbl where val in (${values})
}
Query:
I was going through the doc in the NPM readme.
There queries are done in 2 ways:
await sql.query`select * from mytable where id = ${value}`
2. ```
await new sql.Request().query('select 1 as number')
What is the difference between both, and which one has to be used when?
Blocker:
I am able to run a insert query by
await sql.query`insert into tbl (val1, val2) values (${item}, ${userId})`
// sql is the connection for the global variable as mentioned above
I tried creating the above mentioned query in Transaction. For that I have used this
transaction = new sql.Transaction()
await transaction.begin();
let request = new sql.Request(transaction);
await request.query(/* insert into tbl .... */)
It was working fine, but after some time, when I retried, the query started giving timeout with error Timeout: Request failed to complete in 15000ms
Can't understand why this is happening?
I tried running the same query from the sql server management studio, and it was working as expected