A small utility for generating consistent warning objects across your codebase. It also exposes a utility for emitting those warnings, guaranteeing that they are issued only once (unless configured otherwise).

This module is used by the Fastify framework and it was called fastify-warning prior to version 1.0.0.

npm i process-warning

The module exports two builder functions for creating warnings.

const {
  createWarning,
  createDeprecation
} = require('process-warning')

const warning = createWarning({
  name: 'ExampleWarning',
  code: 'EXP_WRN_001',
  message: 'Hello %s',
  unlimited: true
})
warning('world')

• name (string, required) - The error name, you can access it later with error.name. For consistency, we recommend prefixing module error names with {YourModule}Warning
• code (string, required) - The warning code, you can access it later with error.code. For consistency, we recommend prefixing plugin error codes with {ThreeLetterModuleName}_, e.g. FST_. NOTE: codes should be all uppercase.
• message (string, required) - The warning message. You can also use interpolated strings for formatting the message.
• options (object, optional) - Optional options with the following properties:
  • unlimited (boolean, optional) - Should the warning be emitted more than once? Defaults to false.

This is a wrapper for createWarning. It is equivalent to invoking createWarning with the name parameter set to "DeprecationWarning".

Deprecation warnings have extended support for the Node.js CLI options: --throw-deprecation, --no-deprecation, and --trace-deprecation.

The returned warning function can used for emitting warnings. A warning is guaranteed to be emitted at least once.

• [, a [, b [, c]]] (any, optional) - Parameters for string interpolation.

const { createWarning } = require('process-warning')
const FST_ERROR_CODE = createWarning({ name: 'MyAppWarning', code: 'FST_ERROR_CODE', message: 'message' })
FST_ERROR_CODE()

How to use an interpolated string:

const { createWarning } = require('process-warning')
const FST_ERROR_CODE = createWarning({ name: 'MyAppWarning', code: 'FST_ERROR_CODE', message: 'Hello %s'})
FST_ERROR_CODE('world')

The warning object has methods and properties for managing the warning's state. Useful for testing.

const { createWarning } = require('process-warning')
const FST_ERROR_CODE = createWarning({ name: 'MyAppWarning', code: 'FST_ERROR_CODE', message: 'Hello %s'})
console.log(FST_ERROR_CODE.emitted) // false
FST_ERROR_CODE('world')
console.log(FST_ERROR_CODE.emitted) // true

const FST_ERROR_CODE_2 = createWarning('MyAppWarning', 'FST_ERROR_CODE_2', 'Hello %s')
FST_ERROR_CODE_2.emitted = true
FST_ERROR_CODE_2('world') // will not be emitted because it is not unlimited

How to use an unlimited warning:

const { createWarning } = require('process-warning')
const FST_ERROR_CODE = createWarning({ name: 'MyAppWarning', code: 'FST_ERROR_CODE', message: 'Hello %s', unlimited: true })
FST_ERROR_CODE('world') // will be emitted
FST_ERROR_CODE('world') // will be emitted again

It is possible to suppress warnings by utilizing one of node's built-in warning suppression mechanisms.

Warnings can be suppressed:

• by setting the NODE_NO_WARNINGS environment variable to 1
• by passing the --no-warnings flag to the node process
• by setting '--no-warnings' in the NODE_OPTIONS environment variable

For more information see node's documentation.

Licensed under MIT.