Warnings

Table of contents

• Warnings
  • Warnings In Fastify
  • Fastify Warning Codes
    • FSTWRN001
    • FSTWRN003
    • FSTWRN004
  • Fastify Deprecation Codes
    • FSTDEP022

Warnings

Warnings In Fastify

Fastify uses the Node.js warning event API to notify users of deprecated features and coding mistakes. Fastify's warnings are recognizable by the FSTWRN and FSTDEP prefixes. When encountering such a warning, it is highly recommended to determine the cause using the --trace-warnings and --trace-deprecation flags. These produce stack traces pointing to where the issue occurs in the application's code. Issues opened about warnings without this information will be closed.

Warnings can also be disabled, though it is not recommended. If necessary, use one of the following methods:

• Set the NODE_NO_WARNINGS environment variable to 1
• Pass the --no-warnings flag to the node process
• Set no-warnings in the NODE_OPTIONS environment variable

For more information on disabling warnings, see Node's documentation.

Disabling warnings is not recommended and may cause unexpected behavior.

Fastify Warning Codes

Code	Description	How to solve	Discussion
FSTWRN001	The specified schema for a route is missing. This may indicate the schema is not well specified.	Check the schema for the route.	#4647
FSTWRN003	The %s plugin mixes async and callback styles, which may lead to unhandled rejections.	Do not mix async and callback style.	#6011
FSTWRN004	An errorHandler is being overridden in the same scope, which can lead to subtle bugs.	Avoid calling setErrorHandler more than once in the same scope. For more information, see Server documentation.	#6104

Fastify Deprecation Codes

Deprecation codes are supported by the Node.js CLI options:

• --no-deprecation
• --throw-deprecation
• --trace-deprecation

Code	Description	How to solve	Discussion
FSTDEP022	You are trying to access the deprecated router options on top option properties.	Use options.routerOptions.	#5985