node-postgres/docs/pages/apis/client.mdx

---
title: pg.Client
---

## new Client

`new Client(config: Config)`

Every field of the `config` object is entirely optional. A `Client` instance will use [environment variables](/features/connecting#environment-variables) for all missing values.

```ts
type Config = {
  user?: string, // default process.env.PGUSER || process.env.USER
  password?: string or function, //default process.env.PGPASSWORD
  host?: string, // default process.env.PGHOST
  database?: string, // default process.env.PGDATABASE || user
  port?: number, // default process.env.PGPORT
  connectionString?: string, // e.g. postgres://user:password@host:5432/database
  ssl?: any, // passed directly to node.TLSSocket, supports all tls.connect options
  types?: any, // custom type parsers
  statement_timeout?: number, // number of milliseconds before a statement in query will time out, default is no timeout
  query_timeout?: number, // number of milliseconds before a query call will timeout, default is no timeout
  application_name?: string, // The name of the application that created this Client instance
  connectionTimeoutMillis?: number, // number of milliseconds to wait for connection, default is no timeout
  idle_in_transaction_session_timeout?: number // number of milliseconds before terminating any session with an open idle transaction, default is no timeout
}
```

example to create a client with specific connection information:

```js
const { Client } = require('pg')

const client = new Client({
  host: 'my.database-server.com',
  port: 5334,
  user: 'database-user',
  password: 'secretpassword!!',
})
```

## client.connect

Calling `client.connect` with a callback:

```js
const { Client } = require('pg')
const client = new Client()
client.connect((err) => {
  if (err) {
    console.error('connection error', err.stack)
  } else {
    console.log('connected')
  }
})
```

Calling `client.connect` without a callback yields a promise:

```js
const { Client } = require('pg')
const client = new Client()
client
  .connect()
  .then(() => console.log('connected'))
  .catch((err) => console.error('connection error', err.stack))
```

_note: connect returning a promise only available in pg@7.0 or above_

## client.query

### QueryConfig

You can pass an object to `client.query` with the signature of:

```ts
type QueryConfig {
  // the raw query text
  text: string;

  // an array of query parameters
  values?: Array<any>;

  // name of the query - used for prepared statements
  name?: string;

  // by default rows come out as a key/value pair for each row
  // pass the string 'array' here to receive rows as an array of values
  rowMode?: string;

  // custom type parsers just for this query result
  types?: Types;
}
```

### callback API

```ts
client.query(text: string, values?: any[], callback?: (err: Error, result: QueryResult) => void) => void
```

**Plain text query with a callback:**

```js
const { Client } = require('pg')
const client = new Client()
client.connect()
client.query('SELECT NOW()', (err, res) => {
  if (err) throw err
  console.log(res)
  client.end()
})
```

**Parameterized query with a callback:**

```js
const { Client } = require('pg')
const client = new Client()
client.connect()
client.query('SELECT $1::text as name', ['brianc'], (err, res) => {
  if (err) throw err
  console.log(res)
  client.end()
})
```

### Promise API

If you call `client.query` with query text and optional parameters but **don't** pass a callback, then you will receive a `Promise` for a query result.

```ts
client.query(text: string, values?: any[]) => Promise<Result>
```

**Plain text query with a promise**

```js
const { Client } = require('pg')
const client = new Client()
client.connect()
client
  .query('SELECT NOW()')
  .then((result) => console.log(result))
  .catch((e) => console.error(e.stack))
  .then(() => client.end())
```

**Parameterized query with a promise**

```js
const { Client } = require('pg')
const client = new Client()
client.connect()
client
  .query('SELECT $1::text as name', ['brianc'])
  .then((result) => console.log(result))
  .catch((e) => console.error(e.stack))
  .then(() => client.end())
```

```ts
client.query(config: QueryConfig) => Promise<Result>
```

**client.query with a QueryConfig and a callback**

If you pass a `name` parameter to the `client.query` method, the client will create a [prepared statement](/features/queries#prepared-statements).

```js
const query = {
  name: 'get-name',
  text: 'SELECT $1::text',
  values: ['brianc'],
  rowMode: 'array',
}

client.query(query, (err, res) => {
  if (err) {
    console.error(err.stack)
  } else {
    console.log(res.rows) // ['brianc']
  }
})
```

**client.query with a QueryConfig and a Promise**

```js
const query = {
  name: 'get-name',
  text: 'SELECT $1::text',
  values: ['brianc'],
  rowMode: 'array',
}

// promise
client
  .query(query)
  .then((res) => {
    console.log(res.rows) // ['brianc']
  })
  .catch((e) => {
    console.error(e.stack)
  })
```

**client.query with a `Submittable`**

If you pass an object to `client.query` and the object has a `.submit` function on it, the client will pass it's PostgreSQL server connection to the object and delegate query dispatching to the supplied object. This is an advanced feature mostly intended for library authors. It is incidentally also currently how the callback and promise based queries above are handled internally, but this is subject to change. It is also how [pg-cursor](https://github.com/brianc/node-pg-cursor) and [pg-query-stream](https://github.com/brianc/node-pg-query-stream) work.

```js
const Query = require('pg').Query
const query = new Query('select $1::text as name', ['brianc'])

const result = client.query(query)

assert(query === result) // true

query.on('row', (row) => {
  console.log('row!', row) // { name: 'brianc' }
})
query.on('end', () => {
  console.log('query done')
})
query.on('error', (err) => {
  console.error(err.stack)
})
```

---

## client.end

Disconnects the client from the PostgreSQL server.

```js
client.end((err) => {
  console.log('client has disconnected')
  if (err) {
    console.log('error during disconnection', err.stack)
  }
})
```

Calling end without a callback yields a promise:

```js
client
  .end()
  .then(() => console.log('client has disconnected'))
  .catch((err) => console.error('error during disconnection', err.stack))
```

_note: end returning a promise is only available in pg7.0 and above_

## events

### error

```ts
client.on('error', (err: Error) => void) => void
```

When the client is in the process of connecting, dispatching a query, or disconnecting it will catch and foward errors from the PostgreSQL server to the respective `client.connect` `client.query` or `client.end` callback/promise; however, the client maintains a long-lived connection to the PostgreSQL back-end and due to network partitions, back-end crashes, fail-overs, etc the client can (and over a long enough time period _will_) eventually be disconnected while it is idle. To handle this you may want to attach an error listener to a client to catch errors. Here's a contrived example:

```js
const client = new pg.Client()
client.connect()

client.on('error', (err) => {
  console.error('something bad has happened!', err.stack)
})

// walk over to server, unplug network cable

// process output: 'something bad has happened!' followed by stacktrace :P
```

### end

```ts
client.on('end') => void
```

When the client disconnects from the PostgreSQL server it will emit an end event once.

### notification

Used for `listen/notify` events:

```ts
type Notification {
  processId: number,
  channel: string,
  payload?: string
}
```

```js
const client = new pg.Client()
client.connect()

client.query('LISTEN foo')

client.on('notification', (msg) => {
  console.log(msg.channel) // foo
  console.log(msg.payload) // bar!
})

client.query(`NOTIFY foo, 'bar!'`)
```

### notice

```ts
client.on('notice', (notice: Error) => void) => void
```

Used to log out [notice messages](https://www.postgresql.org/docs/9.6/static/plpgsql-errors-and-messages.html) from the PostgreSQL server.

```js
client.on('notice', (msg) => console.warn('notice:', msg))
```