Operators

Overview of built-in operators and custom operator creation

What are Operators?

Operators are the building blocks of rules in Rule Engine JS. Each operator implements specific logic for comparing, transforming, or validating data.

Rule Engine JS includes 20+ built-in operators organized into 7 categories, plus support for custom operators.

Operator Categories

Comparison

Compare values: eq, neq, gt, gte, lt, lte

Logical

Combine conditions: and, or, not

String

Text operations: contains, startsWith, endsWith, regex

Array

Array membership: in, notIn

Numeric

Number operations: between

Special

Null checks: isNull, isNotNull

State

State changes: changed, changedBy, changedFrom, changedTo, increased, decreased

Quick Reference

Operator	Syntax	Description
eq	{ eq: ['age', 18] }	Equals comparison
gt	{ gt: ['score', 90] }	Greater than
and	{ and: [rule1, rule2] }	Logical AND
or	{ or: [rule1, rule2] }	Logical OR
contains	{ contains: ['name', 'John'] }	String contains
in	{ in: ['admin', 'roles'] }	Array membership
between	{ between: ['age', [18, 65]] }	Range check
changed	{ changed: ['status'] }	Value changed (stateful)

See the Complete Operators Reference for detailed documentation on all operators.

Using Operators

Direct JSON

const rule = {
  and: [
    { gte: ['age', 18] },
    { eq: ['role', 'admin'] }
  ]
};

const result = engine.evaluateExpr(rule, userData);

Rule Helpers

import { createRuleHelpers } from 'rule-engine-js';

const rules = createRuleHelpers();

const rule = rules.and(
  rules.gte('age', 18),
  rules.eq('role', 'admin')
);

const result = engine.evaluateExpr(rule, userData);

Custom Operators

Create custom operators for business-specific logic:

// Register a custom operator
engine.registerOperator('isWorkingAge', (args, context) => {
  const [agePath, country = 'US'] = args;
  const age = context[agePath];

  const minAge = {
    'US': 16,
    'UK': 16,
    'EU': 18
  };

  return age >= (minAge[country] || 18);
});

// Use the custom operator
const rule = { isWorkingAge: ['applicant.age', 'US'] };
const result = engine.evaluateExpr(rule, { applicant: { age: 17 } });

Custom operators integrate seamlessly with built-in operators and rule helpers.

Next Steps

Operators Overview

Complete reference of all operators

Comparison Operators

Detailed comparison operator docs