eomm/fastify-warning

A small utility for creating warnings and emitting them.

fastify-warning

A small utility, used by Fastify itself, for generating consistent warning objects across your codebase and plugins. It also exposes a utility for emitting those warnings, guaranteeing that they are issued only once.

Install

npm i fastify-warning

Usage

The module exports a builder function that returns a utility for creating warnings and emitting them.

const warning = require('fastify-warning')()

Methods

warning.create(name, code, message)

• name (string, required) - The error name, you can access it later with error.name. For consistency, we recommend prefixing plugin error names with FastifWarning{YourPluginName}
• code (string, required) - The warning code, you can access it later with error.code. For consistency, we recommend prefixing plugin error codes with FST_{YourPluginName}_. NOTE: codes should be all uppercase.
• message (string, required) - The warning message. You can also use interpolated strings for formatting the message.

The utility also contains an emit function that you can use for emitting the warnings you have previously created by passing their respective code. A warning is guaranteed to be emitted only once.

warning.emit(code [, a [, b [, c]]])

• code (string, required) - The warning code you intend to emit.
• [, a [, b [, c]]] (any, optional) - Parameters for string interpolation.

const warning = require('fastify-warning')()
warning.create('FastifyWarning', 'FST_ERROR_CODE', 'message')
warning.emit('FST_ERROR_CODE')

How to use an interpolated string:

const warning = require('fastify-warning')()
warning.create('FastifyWarning', 'FST_ERROR_CODE', 'Hello %s')
warning.emit('FST_ERROR_CODE', 'world')

The module also exports an warning.emitted Map, which contains all the warnings already emitted. Useful for testing.

const warning = require('fastify-warning')()
warning.create('FastifyWarning', 'FST_ERROR_CODE', 'Hello %s')
console.log(warning.emitted.get('FST_ERROR_CODE')) // false
warning.emit('FST_ERROR_CODE', 'world')
console.log(warning.emitted.get('FST_ERROR_CODE')) // true

License

Licensed under MIT.