05-optimizing-runtime-with-fact-priorities.mts

/*
 * This is an advanced example that demonstrates using fact priorities to optimize the rules engine.
 *
 * Usage:
 *   node ./examples/05-optimizing-runtime-with-fact-priorities.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/05-optimizing-runtime-with-fact-priorities.js
 */

import "colors";
import { Engine } from "json-rules-engine";
import accountClient from "./support/account-api-client.mjs";

async function start() {
  /**
   * Setup a new engine
   */
  const engine = new Engine();

  /**
   * - Demonstrates setting high performance (cpu) facts higher than low performing (network call) facts.
   */
  const microsoftRule = {
    conditions: {
      all: [
        {
          fact: "account-information",
          operator: "equal",
          value: true,
        },
        {
          fact: "date",
          operator: "lessThan",
          value: 1467331200000, // unix ts for 2016-07-01; truthy when current date is prior to 2016-07-01
        },
      ],
    },
    event: { type: "microsoft-employees" },
  };
  engine.addRule(microsoftRule);

  /**
   * Register listeners with the engine for rule success and failure
   */
  const facts = { accountId: "washington" };
  engine
    .on("success", (event) => {
      console.log(
        facts.accountId +
          " DID ".green +
          "meet conditions for the " +
          event.type.underline +
          " rule.",
      );
    })
    .on("failure", (event) => {
      console.log(
        facts.accountId +
          " did " +
          "NOT".red +
          " meet conditions for the " +
          event.type.underline +
          " rule.",
      );
    });

  /**
   * Low and High Priorities.
   * Facts that do not have a priority set default to 1
   * @type {Integer} - Facts are run in priority from highest to lowest.
   */
  const HIGH = 100;
  const LOW = 1;

  /**
   * 'account-information' fact executes an api call - network calls are expensive, so
   * we set this fact to be LOW priority; it will only be evaluated after all higher priority facts
   * evaluate truthy
   */
  engine.addFact(
    "account-information",
    async (_params, almanac) => {
      // this fact will not be evaluated, because the "date" fact will fail first
      console.log('Checking the "account-information" fact...'); // this message will not appear
      const accountId = await almanac.factValue<string>("accountId");
      return accountClient.getAccountInformation(accountId);
    },
    { priority: LOW },
  );

  /**
   * 'date' fact returns the current unix timestamp in ms.
   * Because this is cheap to compute, we set it to "HIGH" priority
   */
  engine.addFact(
    "date",
    () => {
      console.log('Checking the "date" fact...');
      return Date.now();
    },
    { priority: HIGH },
  );

  // define fact(s) known at runtime
  await engine.run();
}
export default start();

/*
 * OUTPUT:
 *
 * Checking the "date" fact first..
 * washington did NOT meet conditions for the microsoft-employees rule.
 */

/*
 * NOTES:
 *
 * - Notice that the "account-information" fact was never evaluated, saving a network call and speeding up
 * the engine by an order of magnitude(or more!).  Swap the priorities of the facts to see both run.
 */