Module @clipboard-health/rules-engine - v1.17.0

@clipboard-health/rules-engine

A pure functional rules engine to keep logic-dense code simple, reliable, understandable, and explainable.

The engine uses static rules created in code instead of dynamic rules serialized to a database since we haven't needed the latter yet.

npm install @clipboard-health/rules-engine
import { deepEqual } from "node:assert/strict";

import {
all,
allIf,
appendOutput,
firstMatch,
type Rule,
type RuleContext,
} from "@clipboard-health/rules-engine";

interface Input {
a: number;
b: number;
}

interface Output {
result: number;
}

const exampleContext: RuleContext<Input, Output> = {
input: {
a: 2,
b: 5,
},
output: [],
};

const addNumbersIfPositiveRule: Rule<Input, Output> = {
runIf: (input) => input.a > 0 && input.b > 0,
run: (context) => {
const { a, b } = context.input;
return appendOutput(context, { result: a + b });
},
};

const multiplyNumbersIfPositiveRule: Rule<Input, Output> = {
runIf: (input) => input.a > 0 && input.b > 0,
run: (context) => {
const { a, b } = context.input;
return appendOutput(context, { result: a * b });
},
};

const divideNumbersIfNegative: Rule<Input, Output> = {
runIf: (input) => input.a < 0 && input.b < 0,
run: (context) => {
const { a, b } = context.input;
return appendOutput(context, { result: a / b });
},
};

// Using all() applies all the rules to the context
const allResult = all(
addNumbersIfPositiveRule,
divideNumbersIfNegative,
multiplyNumbersIfPositiveRule,
).run(exampleContext);

deepEqual(allResult.output, [{ result: 7 }, { result: 10 }]);

// Using firstMatch() applies the first the rules to the context
const firstMatchResult = firstMatch(
divideNumbersIfNegative,
addNumbersIfPositiveRule,
multiplyNumbersIfPositiveRule,
).run(exampleContext);

deepEqual(firstMatchResult.output, [{ result: 7 }]);

// Using allIf() applies all the rules that return true for `runIf` to the context when the predicate
// (a function received as firs argument) returns true
const allIfResult = allIf(
(input) => input.a === 2,
divideNumbersIfNegative,
addNumbersIfPositiveRule,
multiplyNumbersIfPositiveRule,
).run(exampleContext);

deepEqual(allIfResult.output, [{ result: 7 }, { result: 10 }]);

See package.json scripts for a list of commands.

Interfaces

Rule
RuleContext

Functions

all
allIf
appendOutput
firstMatch