4.0.1 • Public • Published


    NPM Version NPM Downloads Code Style license - APACHE-2.0

    Fastify Plugin to check runtime environment properties

    The purpose of this plugin is to let Fastify web applications do some checks on some properties available at runtime (for example at application startup). By default any checker method that doesn't satisfy its condition will throw Error, but in some cases this is configurable via plugin options.

    Note that all Chechers features exposed here are in the the library check-runtime-env. For Semantic Versioning checks, see semver.


    A common use case is to throw an exception at application startup, if Node.js version is not compatible with the one set in package.json.

    const fastify = require('fastify')()
    const engines = require('../package.json').engines
    // register plugin with some options
    fastify.register(require('fastify-check-runtime-env'), {
      // nodeStrictCheckAtStartup: true, // same as default
      nodeVersionCheckAtStartup: true,
      nodeVersionExpected: engines.node
      // nodeVersionExpected: '<=10.13.0 >=200.0.0', // sample failing test
      // onCheckMismatch: 'exception' // throw an exception // same as default
    // curl => returning the home page, if current Node.js versio in compatible with the expected one

    In the example folder there are some simple server scripts that uses the plugin (inline but it's the same using it from npm registry).


    Fastify ^4.0.1 , Node.js 14 LTS (14.15.0) or later. Note that plugin releases 3.x are for Fastify 3.x, 4.x are for Fastify 4.x, etc. Old plugin releases (0.x) are for Fastify 2.x but are now obsolete.


    Source code is all inside main repo: fastify-check-runtime-env.

    Documentation generated from source code (library API): here.


    The plugin decorate Fastify and expose some functions:

    • CheckRuntimeEnv, the checkers implementation, as a class (RuntimeEnvChecker); but note that to use it you need to wait for this plugin to be fully loaded and initialized

    Plugin options are:

    • onCheckMismatch, define what to do if a checker fails (Node.js version does not match with the expected one, JavaScript not in strict mode, etc); by default 'exception' to raise an Error, but could be 'warning' (to log a message in Fastify logs), or 'exit' (to stop current Node.js process) with exit code 1
    • nodeStrictCheckAtStartup, flag to tell (when true) to check JavaScript strict mode; by default true (safer and already enforced as default mode in modern JavaScript code using classes, ES Modules, etc)
    • nodeVersionCheckAtStartup, flag to tell (when true) to check Node.js version at application startup; by default false
    • 'nodeVersion' the current Node.js version (by default 'process.version')
    • nodeVersionExpected, the semver string with the expected Node.js version (by default empty, so must be manually provided, for example reading 'package.json' attribute 'engines.node' if specified)

    all plugin options are optional, and have a default value.


    Licensed under Apache-2.0.


    npm i fastify-check-runtime-env

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