@kofile/config-factory
v2.1.0
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Config client with optional validation
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ConfigFactory
ConfigFactory is a small helper function that helps you to safely and easily create configuration objects from an externally injected source. You can also pass-in default values and Joi validation schemas, and you'll get easy-to-handle errors if your config object doesn't pass validation.
Usage
The default export is a curried function that expects a map object that translates the from the data you have to the shape you want. Here's a simple example:
// assuming `process.env.SOME_EXISTING_VAR === 'hello world'`
const map = { myCoolNewKey: 'SOME_EXISTING_VAR' }
const configFactory = makeConfigFactory(map)
const config = configFactory(process.env)
config.get(['myCoolNewKey']) === 'hello world'
In your tests, you might not want to muck around with process.env
. Define an object to use instead:
const map = { myCoolNewKey: 'SOME_EXISTING_VAR' }
const configFactory = makeConfigFactory(map)
const config = configFactory({ SOME_EXISTING_VAR: 'hello world' })
config.get(['myCoolNewKey']) === 'hello world'
You can provide a default value as the third value in a tuple:
const map = { myCoolNewKey: ['SOME_EXISTING_VAR', null, 'banans'] }
const configFactory = makeConfigFactory(map)
const config = configFactory({})
config.get(['myCoolNewKey']) === 'bananas'
Also, you can pass in Joi schemas per-key as the second value in a tuple:
const map = { myCoolNewKey: ['SOME_EXISTING_VAR', joi.string().required()] }
const configFactory = makeConfigFactory(map)
const config = configFactory({})
try {
config.get(['myCoolNewKey'])
} catch (error) {
error.message === 'Invalid config for myCoolNewKey!'
}
You can validate your entire config by running the validate()
method:
const map = { myCoolNewKey: ['SOME_EXISTING_VAR', joi.string().required()] }
const configFactory = makeConfigFactory(map)
const config = configFactory({})
config.validate()
This will appear to do nothing, and that's because when called this way, you need to subscribe to the invalid
event handler like so:
config.on('invalid', error => {
console.error(error)
process.exit(1)
})
config.validate()
The event listener will receive error
from the validation result. Get the message of the failure with error.message
.
Subscribing an event handler and invoking config.validate()
is the preferred way of handling configuration validation. The previous method (throwing an error on a property-by-property basis) is only there as a fail-safe against forgetting to invoke validate()
.
Additionally, calling validate()
will skip future checks when calling get
on a keypath.
NOTE: Incomplete or invalid configurations can lead a service to not start at all or start in a thoroughly broken state; therefor it's advisable to bail hard, fast, and noisily with process.exit(1)
if validate()
fails.
Lastly, you can also use computed properties: the function for a computed property will receive the all of the non-computed config as an argument.
NOTE: Order of computed property invocations is not guaranteed, so please don't make computed properties that depend on other computed properties. That just sounds like a headache anyways.
const env = { A: 'aaaa' }
const map = { scarletLetter: 'A', phrase: config => `${config.scarletLetter} is not B`) }
const configFactory = makeConfigFactory(map)
const config = configFactory(process.env)
config.get(['phrase']) === 'aaaa is not B'
You can use computed properties to return hard-coded values:
const map = { theAnswer: () => 42 }
const configFactory = makeConfigFactory(map)
const config = configFactory(process.env)
config.get(['theAnswer']) === 42
Computed properties can also be validated and use default values.
Why?
- Separation of concerns We've described the final shape we want, complete with validations and default values, without hard-coding where the values come from.
- Ease of testing We've full control over the values of
env
without having to fuss with globals. This is a nice side effect of the point above. - State isolation By treating our configuration as the product of inputs into a function, we make it much harder to pass configuration state around via
require
/import
statements. This is a good thing!
Supported Platforms
Node 7+
Testing
Run tests with yarn test