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An error class for Node.js that parses PostgreSQL's ErrorResponse format and sets human readable field names. Works with node-pg, too.
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![NPM version][npm-badge] [npm-badge]:

PgError.js is an error class for Node.js that parses PostgreSQL's ErrorResponse format and names its fields with human readable properties. It's most useful when combined with Brian Carlson's Node.js PostgreSQL client library to get structured and identifiable PostgreSQL errors. Supports all fields returned by PostgreSQL up to v9.4.

The PostgreSQL client library does return an Error object with some fields set, but it's not a dedicated object for easy instanceof identification nor does it yet support all field types. I've found it immensely useful to be strict and classify errors beforehand when building fault tolerant systems. That helps programmatically decide whether to wrap, escalate or handle a particular error.


npm install pg-error

PgError.js follows semantic versioning, so feel free to depend on its major version with something like >= 1.0.0 < 2 (a.k.a ^1.0.0).


var PgError = require("pg-error")

var error = new PgError({
  M: "null value in column \"name\" violates not-null constraint",
  S: "ERROR",
  C: "23502"

error instanceof PgError // => true
error instanceof Error // => true

error.message // => "null value in column \"name\" violates not-null constraint"
error.severity // => "ERROR"
error.code // => 23502

Parsing PostgreSQL's ErrorResponse

var msg = new Buffer("MWash your teeth!\0SWARNING\0\0")
var error = PgError.parse(msg)
error.message // => "Wash your teeth!"
error.severity // => "WARNING"

Using with Node.js PostgreSQL client library

The client does its error and notice parsing on the Pg.Connection object. You can get an active instance of it after connecting from Pg.Client:

var Pg = require("pg")
var pg = new Pg.Client({host: "/tmp", database: "pg_error_test"})
var connection = pg.connection

You'll have to swap out two functions, Pg.Connection.prototype.parseE and Pg.Connection.prototype.parseN, for parsing errors and notices respectively:

connection.parseE = PgError.parse
connection.parseN = PgError.parse

If you want every connection instance to parse errors to PgError, set them on the Pg.Connection prototype:

Pg.Connection.prototype.parseE = PgError.parse
Pg.Connection.prototype.parseN = PgError.parse

However, the way the client is built, it will start emitting those errors and notices under the PgError event name. Until that's improved in the Pg.Connection class, you'll need to re-emit those under the correct error and notice events:

function emitPgError(err) {
  switch (err.severity) {
    case "ERROR":
    case "FATAL":
    case "PANIC": return this.emit("error", err)
    default: return this.emit("notice", err)

connection.on("PgError", emitPgError)

That's it. Your Pg query errors should now be instances of PgError and with all the human readable field names.

Using with Knex.js

Using PgError.js with Knex.js is similar to using it with the plain Node.js PostgreSQL client library described above. Because Knex.js has a connection pool, you'll have to hook PgError.js in on every newly created connection:

  var Knex = require("knex")

    pool: {
      min: 1,
      max: 10,
      afterCreate: function(connection, done) {
        connection.connection.parseE = PgError.parse
        connection.connection.parseN = PgError.parse
        connection.connection.on("PgError", emitPgError)

The emitPgError function is listed above.

Properties on an instance of PgError

For descriptions of the properties, please see PostgreSQL's Error and Notice Message Fields.

Property Field Description
severity S
code C
condition Code name in lowercase according to errcodes.txt.
detail D
hint H
position P Position parsed to a Number.
internalPosition p Internal position parsed to a Number.
internalQuery q
where W
schema s
table t
column c
dataType d
constraint n
file F
line L Line parsed to a Number.
routine R


PgError.js is released under a Lesser GNU Affero General Public License, which in summary means:

  • You can use this program for no cost.
  • You can use this program for both personal and commercial reasons.
  • You do not have to share your own program's code which uses this program.
  • You have to share modifications (e.g. bug-fixes) you've made to this program.

For more convoluted language, see the LICENSE file.


Andri Möll typed this and the code.
Monday Calendar supported the engineering work.

If you find PgError.js needs improving, please don't hesitate to type to me now at or create an issue online.

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