feature-helper
This library is a helper to abstract all different sources of feature flag services on your application. Regardless of any feature flag source, format, or type, it can help you connect to one API in order to work with feature flags in runtime.
The library is written in TypeScript and is compatible for use with JavaScript as well.
Installation
yarn add @bills/feature-helper
or
npm i @bills/feature-helper --save
Usage
TypeScript syntax - You can import the interfaces as well
;
EcmaScript 2015 syntax
import { FeatureFlagHelper } from '@bills/feature-helper';
EcmaScript5 syntax
var FeatureHelper = ;var FeatureFlagHelper = FeatureHelperFeatureFlagHelper;
Pass your feature flag sources to the constructor method in an array. The Flag sources need to implement the IFeatureSource interface.
<T>
fetcher - TFetcher;
The Fetcher Function is a function that can asynchronously retrieve all feature flag data. This may be a remote call, a database read, etc... What it is does not matter to the library. All that matters is that is returns a promise, and the type that gets resolved in the promise is of generic type T. Type T is important for the Transformer function, explained below.
<T>
transformer - TTransfomer;;
The Transformer Function takes the result of the fetcher call (the type was generic T, remember?), and translates it into an array of IFeatures.
IFeature is pretty simple: name
of the feature flag, the source
it came from, and the value
. Most likely,
the value will be a boolean, but some feature flags do have other types such as string, number, or object.
So...
Construct the class like the following
; ;
NOTE: Validation
The IFeatureSource fields are extremely important and they will be validated at the constructor. If they are invalid, the constructor will throw an Error.
You can check it by calling FeatureFlagHelper.isValidFeatureSource(mySource)
and retrieve a boolean.