📏 Ruls

Typesafe rules engine with JSON encoding

Features

• Intuitive interface
• JSON-encodable rules
• Compatible with all type validation libraries

Setup

Install ruls with your package manager of choice:

npm	npm install ruls
Yarn	yarn add ruls
pnpm	pnpm add ruls

Once complete, you can import it with:

import {rule, signal} from 'ruls';

Also, bring your favorite validation library (e.g. zod):

import {z} from 'zod';

Usage

type Context = {
  user: {
    age: number;
    isActive: boolean;
    username: string;
    hobbies: Array<string>;
  };
};

const signals = {
  age: signal.type(z.number()).value<Context>(({user}) => user.age),
  isActive: signal.type(z.boolean()).value<Context>(({user}) => user.isActive),
  username: signal.type(z.string()).value<Context>(({user}) => user.username),
  hobbies: signal
    .type(z.array(z.string()))
    .value<Context>(({user}) => user.hobbies),
};

const programmers = rule.every([
  signals.age.greaterThanOrEquals(18),
  signals.isActive.isTrue(),
  signals.username.startsWith('user'),
  signals.hobbies.contains('programming'),
]);

const isEligible = await programmers.evaluate({
  user: {
    age: 25,
    isActive: true,
    username: 'user123',
    hobbies: ['reading', 'programming', 'traveling'],
  },
});

Context

The contextual data or state relevant for evaluating rules. It encapsulates the necessary information required by signals to make decisions and determine the outcome of rules.

Example

type Context = {
  user: {
    age: number;
    isActive: boolean;
    username: string;
    hobbies: Array<string>;
  };
};

Signal

A specific piece of information used to make decisions and evaluate rules. It acts as a building block for defining conditions and comparisons in the rule expressions. Signals encapsulate the logic and operations associated with specific data types, allowing you to perform comparisons, apply operators, and define rules based on the values they represent.

Example

const signals = {
  age: signal.type(z.number()).value<Context>(({user}) => user.age),
  isActive: signal.type(z.boolean()).value<Context>(({user}) => user.isActive),
  username: signal.type(z.string()).value<Context>(({user}) => user.username),
  hobbies: signal
    .type(z.array(z.string()))
    .value<Context>(({user}) => user.hobbies),
};

These modifiers and operators apply to all signal types:

Modifier	Description	Encoded
not	Inverts the operator result	{$not: rule}

Operator	Description	Encoded
equals	Matches the exact value	{$eq: value}
in	Matches if the value in the list	{$in: [...values]}

string type

Operator	Description	Encoded
includes	Matches if the string includes a specific value	{$inc: value}
startsWith	Matches if the string starts with a specific value	{$pfx: value}
endsWith	Matches if the string ends with a specific value	{$sfx: value}
matches	Matches the string using a regular expression	{$rx: regex}

number type

Operator	Description	Encoded
lessThan	Matches if the number is less than a specific value	{$lt: value}
lessThanOrEquals	Matches if the number is less than or equal to a specific value	{$lte: value}
greaterThan	Matches if the number is greater than a specific value	{$gt: value}
greaterThanOrEquals	Matches if the number is greater than or equal to a specific value	{$gte: value}

boolean type

Operator	Description	Encoded
isTrue	Matches if the boolean is true	{$eq: true}
isFalse	Matches if the boolean is false	{$eq: false}

Array type

Operator	Description	Encoded
every	Matches if all of the array elements passes the rule	{$and: [rule]}
some	Matches if at least one of the array elements passes the rule	{$or: [rule]}
contains	Matches if the array contains the specific value	{$all: [value]}
containsEvery	Matches if array contains all of the specific values	{$all: [...values]}
containsSome	Matches if array contains at least one of the specific values	{$any: [...values]}

Rule

Allows you to define complex conditions and criteria for decision-making. It consists of one or more signals, which can be combined using logical operators to create intricate structures.

Example

const programmers = rule.every([
  signals.age.greaterThanOrEquals(18),
  signals.isActive.isTrue(),
  signals.username.startsWith('user'),
  signals.hobbies.contains('programming'),
]);

Combination

Operator	Description	Encoded
every	Matches if all of the rules pass	{$and: [...rules]}
some	Matches if at least one of the rules pass	{$or: [...rules]}
none	Matches if none of the rules pass	{$not: {$or: [...rules]}}

Encoding

Rules can be encoded into objects and/or JSON. That makes it possible to store them on a database for runtime retrieval.

const check = rule.every([
  signals.sampleString.matches(/3$/g),
  signals.sampleArray.not.contains(246),
]);

// Encoding
const encodedCheck = check.encode(signals);
expect(encodedCheck).toEqual({
  $and: [{sampleString: {$rx: '/3$/g'}}, {$not: {sampleArray: {$all: [246]}}}],
});
expect(JSON.stringify(encodedCheck)).toEqual(
  '{"$and":[{"sampleString":{"$rx":"/3$/g"}},{"$not":{"sampleArray":{"$all":[246]}}}]}',
);

// Decoding
const parsedCheck = await rule.parse(encodedCheck, signals);
expect(parsedCheck.encode(signals)).toEqual(encodedCheck);