Warnings
- Warnings

Warnings

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Warnings

Warnings

Warnings In Fastify

Fastify utilizes Node.js’s warning event API to notify users of deprecated features and known coding mistakes. Fastify’s warnings are recognizable by the FSTWRN and FSTDEP prefixes on warning code. When encountering such a warning, it is highly recommended that the cause of the warning be determined through use of the --trace-warnings and --trace-deprecation flags. These will produce stack traces pointing out where the issue occurs in the application’s code. Issues opened about warnings without including this information may be closed due to lack of information.

In addition to tracing, warnings can also be disabled. It is not recommended to disable warnings as a matter of course, but if necessary, they can be disabled by using any of the following methods:

setting the NODE_NO_WARNINGS environment variable to 1
passing the --no-warnings flag to the node process
setting ‘no-warnings’ in the NODE_OPTIONS environment variable

For more information on how to disable warnings, see node’s documentation.

However, disabling warnings is not recommended as it may cause potential problems when upgrading Fastify versions. Only experienced users should consider disabling warnings.

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
FSTWRN002	The %s plugin being registered mixes async and callback styles, which will result in an error in `fastify@5`.	Do not mix async and callback style.	#5139

Fastify Deprecation Codes

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

Code	Description	How to solve	Discussion
FSTDEP005	You are accessing the deprecated `request.connection` property.	Use `request.socket`.	#2594
FSTDEP006	You are decorating Request/Reply with a reference type. This reference is shared amongst all requests.	Do not use Arrays/Objects as values when decorating Request/Reply.	#2688
FSTDEP007	You are trying to set a HEAD route using `exposeHeadRoute` route flag when a sibling route is already set.	Remove `exposeHeadRoutes` or explicitly set `exposeHeadRoutes` to `false`	#2700
FSTDEP008	You are using route constraints via the route `{version: “…”}` option.	Use `{constraints: {version: “…”}}` option.	#2682
FSTDEP009	You are using a custom route versioning strategy via the server `{versioning: “…”}` option.	Use `{constraints: {version: “…”}}` option.	#2682
FSTDEP010	Modifying the `reply.sent` property is deprecated.	Use the `reply.hijack()` method.	#3140
FSTDEP011	Variadic listen method is deprecated.	Use `.listen(optionsObject)`.	#3712
FSTDEP012	You are trying to access the deprecated `request.context` property.	Use `request.routeOptions.config` or `request.routeOptions.schema`.	#4216 #5084
FSTDEP013	Direct return of “trailers” function is deprecated.	Use “callback” or “async-await” for return value.	#4380
FSTDEP014	You are trying to set/access the default route. This property is deprecated.	Use `setNotFoundHandler` if you want to custom a 404 handler or the wildcard (`*`) to match all routes.	#4480
FSTDEP015	You are accessing the deprecated `request.routeSchema` property.	Use `request.routeOptions.schema`.	#4470
FSTDEP016	You are accessing the deprecated `request.routeConfig` property.	Use `request.routeOptions.config`.	#4470
FSTDEP017	You are accessing the deprecated `request.routerPath` property.	Use `request.routeOptions.url`.	#4470
FSTDEP018	You are accessing the deprecated `request.routerMethod` property.	Use `request.routeOptions.method`.	#4470
FSTDEP019	You are accessing the deprecated `reply.context` property.	Use `reply.routeOptions.config` or `reply.routeOptions.schema`.	#5032 #5084
FSTDEP020	You are using the deprecated `reply.getReponseTime()` method.	Use the `reply.elapsedTime` property instead.	#5263
FSTDEP021	The `reply.redirect()` method has a new signature: `reply.redirect(url: string, code?: number)`. It will be enforced in `fastify@v5`‘.	#5483
FSTDEP022	You are using the deprecated json shorthand schema on route %s. Specify full object schema instead. It will be removed in `fastify@v5`	#5483