JSON Rules: Change Logic, Skip the Rebuild

#json #react #javascript #productivity

Your Business Logic Doesn't Belong in Code

Hey there! Let me ask you something: how many times have you deployed an app just to change one tiny rule?

"Users need to be 21 now, not 18."
"Actually, gold members get 15% off, not 10%."

Rebuild. Redeploy. Wait. Repeat.

There's a better way.

What If Rules Were Just... Data?

Instead of this:

if (user.age >= 18 && user.tier === 'gold') {
  applyDiscount();
}

You write this:

const discountRule = {
  and: [
    { gte: ['user.age', 18] },
    { eq: ['user.tier', 'gold'] }
  ]
};

See the difference? The second one is just JSON. You can store it in a database, fetch it from an API, or update it without touching your code.

That's exactly what rule-engine-js does.

Quick Example

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

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

const canAccessPremium = rules.and(
  rules.gte('user.age', 18),
  rules.eq('user.verified', true)
);

const user = { age: 25, verified: true };
engine.evaluateExpr(canAccessPremium, user).success; // true

Clean, right?

TypeScript? We Got You

Here's my favorite part. If you're using TypeScript, you get full path autocomplete:

interface UserContext {
  user: { name: string; age: number };
  order: { total: number; status: string };
}

const rules = createRuleHelpers<UserContext>();

// Start typing 'user.' and your IDE suggests: name, age
rules.gte('user.age', 18);      // ✓ autocomplete works
rules.gte('user.name', 18);     // ✗ TypeScript yells at you (name isn't a number!)