5 Lines of Code That Replace 100 Lines of Business Logic

Table of Contents

• The Before/After That Will Blow Your Mind
• We’ve All Been Here
• The Magic Moment That Changed Everything
• Try This Right Now (30 Seconds)
• Three Superpowers That Will Change Your Life
  • Superpower 1: Dynamic Field Comparison
  • Superpower 2: Zero Dependencies + Lightning Fast
  • Superpower 3: Production-Ready Security
• Your Real-World Use Cases
  • Form Validation That Doesn’t Suck
  • User Access Control (The Clean Way)
  • Dynamic Pricing (Without The Headache)
• Framework? We Don’t Care About Your Framework
• The Challenge: I Dare You To Try This
• The Proof Is In The Pudding
• Your Next 5 Minutes

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The Before/After That Will Blow Your Mind

// ❌ BEFORE: 100+ lines of spaghetti code nightmare
function canUserAccessResource(user, resource, order) {
  if (!user) return false;
  if (!user.active) return false;
  if (user.status === 'banned' || user.status === 'suspended') return false;
  if (!user.emailVerified) return false;

  if (user.age < 18) return false;
  if (user.role === 'admin') return true;

  if (user.role === 'user') {
    if (!user.permissions || !Array.isArray(user.permissions)) return false;
    if (!user.permissions.includes('read')) return false;

    if (resource.sensitivity === 'high') {
      if (!user.permissions.includes('sensitive_data')) return false;
      if (user.clearanceLevel < 3) return false;
    }

    if (order && order.total > 1000) {
      if (user.accountAge < 30) return false;
      if (!user.verifiedIdentity) return false;
    }

    if (user.department !== resource.department) {
      if (!user.crossDepartmentAccess) return false;
    }

    // ... 60+ more lines of nested conditions
  }

  return false;
}

// ✅ AFTER: 5 clean, readable lines with Rule Engine JS
const accessRule = rules.and(
  rules.validation.activeUser('user'),
  rules.gte('user.age', 18),
  rules.or(
    rules.eq('user.role', 'admin'),
    rules.and(rules.in('read', 'user.permissions'), rules.departmentAccess('user', 'resource')),
  ),
);

const canAccess = engine.evaluate(accessRule, { user, resource, order });

What if I told you this messy business logic that’s killing your codebase could be 5 readable lines instead?

We’ve All Been Here

Picture this: It’s Friday afternoon. The product manager slides into your DMs with those dreaded words: “Hey, can you just add one tiny condition to the user access logic?”

You open the file. 200 lines of nested if statements stare back at you. Comments from 3 different developers. Business logic scattered across 7 different functions. You die a little inside.

Sound familiar? 😭

Every developer has that one function. You know the one:

• Started as “simple user validation”
• Now handles 47 different edge cases
• Nobody wants to touch it
• Breaks every time someone sneezes
• Takes 30 minutes to understand what it actually does

The Magic Moment That Changed Everything

Here’s what made me build Rule Engine JS. I was working on an e-commerce platform when the business team dropped this bomb:

“We need to update discount rules every week without deploying code.”

That’s when it hit me: What if business logic could live in the database as simple JSON?

// Store rules as JSON in your database
const discountRule = {
  or: [
    {
      and: [{ eq: ['customer.type', 'vip'] }, { gte: ['order.total', 100] }],
    },
    { gte: ['customer.loyaltyPoints', 1000] },
    {
      and: [{ eq: ['customer.isFirstTime', true] }, { gte: ['order.total', 50] }],
    },
  ],
};

// Business team updates rules WITHOUT touching code
await updateRule('discount-eligibility', newRules);

// Your app instantly uses the new logic
const result = engine.evaluate(loadedRule, customerData);

Zero deployments. Zero downtime. Zero developer headaches.

Try This Right Now (30 Seconds)

npm install rule-engine-js

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

const engine = createRuleEngine();
const rules = createRuleHelpers();

// Test it with the alcohol purchase rule
const canBuyAlcohol = rules.gte('age', 21);

console.log(engine.evaluate(canBuyAlcohol, { age: 25 })); // true
console.log(engine.evaluate(canBuyAlcohol, { age: 19 })); // false

// Your first "holy shit" moment starts now

That’s it. No configuration. No setup. Just working code.

Three Superpowers That Will Change Your Life

🔥 Superpower 1: Dynamic Field Comparison

Most rule engines make you jump through hoops to compare fields. We make it natural:

// Compare ANY fields in your data
const orderValidation = rules.and(
  rules.field.lessThan('order.total', 'user.creditLimit'),
  rules.field.equals('password', 'confirmPassword'),
  rules.field.greaterThan('user.accountAge', 'security.minimumAge'),
);

// Works with nested objects automatically
const profileCheck = rules.field.equals('user.email', 'backup.recoveryEmail');

Other rule engines: “Write custom validators and hope they work”
Rule Engine JS: “Just tell us what to compare”

⚡ Superpower 2: Zero Dependencies + Lightning Fast

// Bundle size: 24KB (smaller than most images)
// Evaluation time: <1ms (faster than a database query)
// Dependencies: 0 (your security team will love you)
// Node.js versions: 16+ (just works everywhere)

Your app stays lean. Your builds stay fast. Your deploys stay simple.

🛡️ Superpower 3: Production-Ready Security

We handle the nightmare scenarios so you don’t have to:

// Built-in protection against:
// ✅ Prototype pollution attacks
// ✅ Code injection attempts
// ✅ DoS attacks via complex rules
// ✅ Function execution exploits

// This malicious input fails safely:
const maliciousData = {
  __proto__: { isAdmin: true },
  constructor: { prototype: { hasAccess: true } },
};

engine.evaluate(rule, maliciousData); // Secure, no exploits possible

Sleep better knowing your rule engine isn’t a security hole.

Your Real-World Use Cases

Form Validation That Doesn’t Suck

const formRules = rules.and(
  rules.validation.required('email'),
  rules.validation.email('email'),
  rules.field.equals('password', 'confirmPassword'),
  rules.validation.ageRange('age', 18, 120),
  rules.isTrue('agreedToTerms'),
);

// One rule handles your entire form
const isValid = engine.evaluate(formRules, formData);

User Access Control (The Clean Way)

const accessRule = rules.and(
  rules.isTrue('user.active'),
  rules.or(
    rules.eq('user.role', 'admin'),
    rules.and(
      rules.eq('user.department', 'resource.department'),
      rules.in('read', 'user.permissions'),
    ),
  ),
);

// Express middleware in 3 lines
app.get('/sensitive-data', (req, res, next) => {
  const hasAccess = engine.evaluate(accessRule, { user: req.user, resource });
  hasAccess ? next() : res.status(403).json({ error: 'Access denied' });
});

Dynamic Pricing (Without The Headache)

const pricingRule = rules.or(
  // VIP discount
  rules.and(rules.eq('customer.tier', 'vip'), rules.gte('order.total', 100)),
  // Loyalty discount
  rules.gte('customer.points', 1000),
  // First-time customer
  rules.and(rules.isTrue('customer.firstTime'), rules.gte('order.total', 50)),
);

// Business team updates pricing rules via admin panel
// Zero developer involvement

Framework? We Don’t Care About Your Framework

React? ✅ Perfect
Vue? ✅ Works great
Express? ✅ Love it
Next.js? ✅ No problem
Vanilla JS? ✅ Obviously
Your weird internal framework? ✅ Probably fine

// React component
function UserProfile({ user }) {
  const canEdit = engine.evaluate(editRule, { user, currentUser });
  return (
    <div>
      <h1>{user.name}</h1>
      {canEdit && <button>Edit Profile</button>}
    </div>
  );
}

// Vue computed property
computed: {
  userCanAccess() {
    return engine.evaluate(this.accessRule, this.userData);
  }
}

// Express middleware
const checkAccess = (rule) => (req, res, next) => {
  engine.evaluate(rule, req.user) ? next() : res.status(403).end();
};

The Challenge: I Dare You To Try This

Here’s my challenge: Take your messiest business logic function. The one that makes junior developers cry. The one with 47 nested conditions.

Time yourself:

1. ⏱️ 5 minutes to install Rule Engine JS
2. ⏱️ 10 minutes to rewrite that function as rules
3. ⏱️ Watch your code become readable for the first time in months

I bet you’ll:

• Cut your code by 60-80%
• Actually understand what the logic does
• Want to rewrite every other business rule in your app
• Wonder why you didn’t do this years ago

The Proof Is In The Pudding

// Before: 47 lines, 6 nested levels, 3 bugs, 0 tests
function canUserDoThing(user, thing, context) {
  // ... 47 lines of hell
}

// After: 8 lines, readable, testable, maintainable
const canDoThingRule = rules.and(
  rules.validation.activeUser('user'),
  rules.or(
    rules.eq('user.role', 'admin'),
    rules.and(
      rules.in('thing.permission', 'user.permissions'),
      rules.field.greaterThan('user.level', 'thing.requiredLevel'),
    ),
  ),
);

const result = engine.evaluate(canDoThingRule, { user, thing, context });

Same logic. 85% less code. 100% more sanity.

Your Next 5 Minutes

Ready to stop hating your business logic?

⭐ Star the repo: github.com/crafts69guy/rule-engine-js (seriously, this helps)

🚀 Try it now: npm install rule-engine-js

📚 Read the docs: Complete examples and patterns included

💬 Tell me your story: What business logic nightmare did you solve? I want to hear about your wins!

🐛 Found an issue? Open a GitHub issue - I actually respond to them

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Built by a developer who was tired of business logic spaghetti. Zero dependencies, maximum developer happiness.

P.S. - If you’re still writing 100-line business logic functions in 2024, your future self will thank you for making the switch. Trust me on this one.