regent
v3.6.0
Published
Javascript rules engine
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Regent: Business Rules in JavaScript
Regent lets you query a data structure by asking true or false questions. Regent logic is written as single responsibility rules that are self-documenting, composable, and human readable. Let's look at an example.
import { equals } from 'regent';
// return a function that evaluates to true
// if prop `isRaining` is equal to true
const isRaining = equals('@isRaining', true);
// Define your data structure
const data = { isRaining: true };
// Evaluate the rule
const isUmbrellaNeeded = isRaining(data); // true
equals
predicate documentation
Taking the previous example a bit further, we can refine the scenario to be more precise. We can create and combine multiple rules to test this condition
If it is raining and the wind isn't so strong the umbrella will turn inside-out and blow out of our hands, we need an umbrella.
import { and, equals, lessThan } from 'regent';
// Define a rule for `isRaining` and a rule for `isCalm`.
// Use regent and to compose them together
const isRaining = equals('@isRaining', true);
const isCalm = lessThan('@windSpeedInMph', 25);
const isRainingAndCalm = and(isRaining, isCalm);
// Define your data structure
const data = { isRaining: true, windSpeedInMph: 20 };
// Evaluate the rule
isRainingAndCalm(data); // true
Regent also provides a simple way to find or filter array items based on a regent rule.
import { equals, lessThan, find, filter } from 'regent';
const isRaining = equals('@isRaining', true);
const isSunny = lessThan('@cloudCover', 10);
const isCold = lessThan('@temperature', 60);
const data = {
isRaining: false,
cloudCover: 0,
temperature: 42
};
const items = [
{ item: 'Winter hat', rule: isCold },
{ item: 'Sunglasses', rule: isSunny },
{ item: 'Umbrella', rule: isRaining },
]
// filter will return an array with the Winter Hat and Sunglasses objects
// because it is cold and sunny
// [{ item: 'Winter hat', rule: isCold }, { item: 'Sunglasses', rule: isSunny }]
filter(items, data)
Installation
npm install --save regent
Documentation
License
MIT