Rules Engine

JavaScript rules engine for validating data object structures.

Table of Contents

• Features
• Installation
• Usage
  • Default Engine
  • Override Engine
  • Default Operators
  • Customizing Operators
  • Rule Conditions
  • Persisting Rules
• Development

Features

• 💪 Easy to use chainable API.
• 💥 Support for infinitely nested AND / OR conditions.
• 🚀 Rules can be expressed in simple JSON.
• ✔️ Customize operators with your own functions.
• 🏄 Access nested properties with dot notation paths.

Installation

npm install js-rules-engine --save

Usage

import { Rule } from 'js-rules-engine';

// homeWorld.name equals 'Tatooine' AND (name contains 'Skywalker' OR eyeColor is 'green')
const rule = new Rule().equals('homeWorld.name', 'Tatooine').or((sub) => {
  sub.contains('name', 'Skywalker').equals('eyeColor', 'green');
});

// object of data to evaluate rule against
const fact = {
  eyeColor: 'blue',
  homeWorld: {
    name: 'Tatooine',
  },
  name: 'Luke Skywalker',
};

rule.evaluate(fact);
// => true

Default Engine

An Engine contains all operators available to a Rule. By default, a single Engine instance is used for all Rule instances. The default Engine's operators can be customized like this:

import { defaultEngine } from 'js-rules-engine';

defaultEngine.removeOperator('greaterThan');
defaultEngine.addOperator('moreGreaterThan', myAwesomeFunction);

Override Engine

Each instance of Rule has the ability to use it's own Engine instance, overriding the default.

import { Engine, Rule } from 'js-rules-engine';

const engine = new Engine();
const rule = new Rule(null, engine);

Default Operators

Each Engine contains the follow operators by default:

• equals
• notEquals
• in
• notIn
• contains
• notContains
• lessThan
• lessThanOrEquals
• greaterThan
• greaterThanOrEquals

Customizing Operators

Add your own operators to an Engine. Once added, any custom Operator can be used via the Rule's add() method.

import { defaultEngine, Operator } from 'js-rules-engine';

const noop = new Operator('noop', (a, b) => true);
defaultEngine.addOperator(noop);

You can also remove an Operator.

import { defaultEngine } from 'js-rules-engine';

defaultEngine.removeOperator('noop');

Rule Conditions

The add method is a generic way to add a condition to the Rule. The conditions operator is added via it's name. The value type should match what the operator is expecting.

Param	Description	Type
fact	Property name or dot notation path.	string
operator	Name of operator to use.	string
value	Value to compare.	any

A Rule has shortcut methods for all default operators. Each method takes two arguments (fact and value) and returns the Rule instance for chaining.

Method	Fact Type	Value Type
equals	string	any
notEquals	string	any
in	string	string
notIn	string	string
contains	string	any
notContains	string	any
lessThan	string	number
lessThanOrEquals	string	number
greaterThan	string	number
greaterThanOrEquals	string	number

Nested conditions can be achieved with the and() / or() methods. Each methods takes one parameter, a callback function that is supplied with a nested Rule instance as the first argument, and returns the original Rule instance for chaining.

Persisting Rules

Rules can easily be converted to JSON and persisted to a database, file system, or elsewhere.

// save rule as JSON string ...
const jsonString = JSON.stringify(rule);
localStorage.setItem('persistedRule', jsonString);

// ... and hydrate rules from a JSON object!
const jsonString = localStorage.getItem('persistedRule');
const json = JSON.parse(jsonString);
const rule = new Rule(json);

Example JSON structure:

{
  "and": [
    {
      "fact": "homeWorld.name",
      "operator": "equals",
      "value": "Tatooine"
    },
    {
      "or": [
        {
          "fact": "name",
          "operator": "contains",
          "value": "Skywalker"
        },
        {
          "fact": "eyeColor",
          "operator": "equals",
          "value": "green"
        }
      ]
    }
  ]
}

Development

npm install
npm run build