PostgreSQL has a rich system of supported data types. node-postgres does its best to support the most common data types out of the box and supplies an extensible type parser to allow for custom type serialization and parsing.

strings by default

node-postgres will convert a database type to a JavaScript string if it doesn't have a registered type parser for the database type. Furthermore, you can send any type to the PostgreSQL server as a string and node-postgres will pass it through without modifying it in any way. To circumvent the type parsing completely do something like the following.

const queryText = 'select int_col::string, date_col::string, json_col::string from my_table'
const result = await client.query(queryText)

console.log(result.rows[0]) // will contain the unparsed string value of each column

type parsing examples

uuid + json / jsonb

There is no data type in JavaScript for a uuid/guid so node-postgres converts a uuid to a string. JavaScript has great support for JSON and node-postgres converts json/jsonb objects directly into their JavaScript object via JSON.parse. Likewise sending an object to the PostgreSQL server via a query from node-postgres, node-posgres will call JSON.stringify on your outbound value, automatically converting it to json for the server.

const createTableText = `

  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  data JSONB
// create our temp table
await client.query(createTableText)

const newUser = { email: 'brian.m.carlson@gmail.com' }
// create a new user
await client.query('INSERT INTO users(data) VALUES($1)', [newUser])

const { rows } = await client.query('SELECT * FROM users')

  id: 'd70195fd-608e-42dc-b0f5-eee975a621e9',
  data: { email: 'brian.m.carlson@gmail.com' }

date / timestamp / timestamptz

node-postgres will convert instances of JavaScript date objects into the expected input value for your PostgreSQL server. Likewise, when reading a date, timestamp, or timestamptz column value back into JavaScript, node-postgres will parse the value into an instance of a JavaScript Date object.

const createTableText = `
  date_col DATE,
  timestamp_col TIMESTAMP,
  timestamptz_col TIMESTAMPTZ,
// create our temp table
await client.query(createTableText)

// insert the current time into it
const now = new Date()
const insertText = 'INSERT INTO dates(date_col, timestamp_col, timestamtz_col'
await client.query(insertText, [now, now, now])

// read the row back out
const result = await client.query('SELECT * FROM dates')

// {
// date_col: 2017-05-29T05:00:00.000Z,
// timestamp_col: 2017-05-29T23:18:13.263Z,
// timestamptz_col: 2017-05-29T23:18:13.263Z
// }

psql output:

bmc=# select * from dates;
  date_col  |      timestamp_col      |      timestamptz_col
 2017-05-29 | 2017-05-29 18:18:13.263 | 2017-05-29 18:18:13.263-05
(1 row)

node-postgres converts DATE and TIMESTAMP columns into the local time of the node process set at process.env.TZ.

note: I generally use TIMESTAMPTZ when storing dates; otherwise, inserting a time from a process in one timezone and reading it out in a process in another timezone can cause unexpected differences in the time.

Although PostgreSQL supports microseconds in dates, JavaScript only supports dates to the millisecond precision. Keep this in mind when you send dates to and from PostgreSQL from node: your milliseconds will be truncated when converting to a JavaScript date object even if they exist in the database. If you need to preserve them, I recommend using a custom type parser.
made withby@briancarlson