pg: typescript error after retrieving a client from the connection pool

import pg, {PoolConfig} from 'pg';
const { Pool } = pg;

const pool = new Pool({
    user: process.env.USER_NAME,
    host: process.env.HOST_NAME,
    database: process.env.DATABASE,
    password: process.env.PASSWORD,
    port: process.env.DB_PORT
} as PoolConfig);

export {
    pool
};

I am trying to retrieve a client from the postgresql connection pool and am receiving a type error when I call "client.query". I am receiving the following error for the ".query" function, "TS2339: Property 'query' does not exist on type 'void'". This is a typescript node.js application.

const client = await pool.connect();

try {
    const res = await client.query('SELECT …’, [….]);

    if (!res?.rows[0])
        return null;

    return res.rows[0];
} catch (e) {
    throw e;
} finally {
    client.release();
}

This is my tsconfig.json file:

{
    "compilerOptions": {
        "module": "commonjs",
        "target": "es6",
        "strict": true,
        "sourceMap": true,
        "outDir": "build",
        "moduleResolution": "node",
        "resolveJsonModule": true,
        "lib": ["es2017"],
        "allowSyntheticDefaultImports": true,
        "skipLibCheck": true
    },
    "files": [
        "./node_modules/@types/node/index.d.ts"
    ],
    "exclude": [
        "node_modules",
        "build"
    ],
    "include": [
        "**/*.ts"
    ]
}

I also added the package @types/pg and am not sure what could be missing.

Assuming what you're showing is not an exact 1:1 copy of the code that actually caused the error: I would expect this to happen if you attempted to mix your connect() calls by:

• duplicating the connect() call somewhere, leading to pool.connect() returning a client, which you again call connect() on, which promises a void.

• trying to run one query when acquiring the connection from the pool, by giving connect() a callback function as argument:
  >pool.connect(callback: (...) => void) => void

  then trying to use that connect() result as a pg.Client to run another query, even though in this scenario it's void as indicated by the message and pointed out by qrsngky. pool.connect() promises to bring back a client only when called without any arguments.
  >pool.connect() => Promise<pg.Client>

  One use case that comes to mind for this would be some kind of connection setup script - you could handle it .on() connect or acquire events.

• exposing an altered/overloaded connect() when exporting from the module where you've configured and initialised the pool, making a seemingly no-arg call default to the form using a callable or duplicating the call. So either of the above, just elsewhere, hidden away.

A few double checks could be helpful, too: are you sure the pool you exported is the same thing you're calling connect() on later? Is pg package the one you expect, the version you expect?

As a workaround, regardless of what caused this: if you're not defining transactions inside your query, you could try to use pool.query() directly:

const res = await pool.query('SELECT …', [….]);
if (!res?.rows[0])
    return null;
return res.rows[0];

No need to acquire the client from the pool through connect() first, then finally {client.release();} later because pool.query() handles both automatically. Since the catch only re-throws the error and finally only releases the connection, the entire try block could be removed. That's actually what the package author recommends:
>I find pool.query to be a handy shortcut many situations and use it exclusively unless I need a transaction.