Function start

examples/08-fact-comparison.js:15–130

()

const { Engine } = require('json-rules-engine')

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

  /**
   * Rule for determining if account has enough money to purchase a $50 gift card product
   *
   * customer-account-balance >= $50 gift card
   */
  const rule = {
    conditions: {
      all: [{
        // extract 'balance' from the 'customer' account type
        fact: 'account',
        path: '$.balance',
        params: {
          accountType: 'customer'
        },

        operator: 'greaterThanInclusive', // >=

        // "value" in this instance is an object containing a fact definition
        // fact helpers "path" and "params" are supported here as well
        value: {
          fact: 'product',
          path: '$.price',
          params: {
            productId: 'giftCard'
          }
        }
      }]
    },
    event: { type: 'customer-can-afford-gift-card' }
  }
  engine.addRule(rule)

  engine.addFact('account', (params, almanac) => {
    // get account list
    return almanac.factValue('accounts')
      .then(accounts => {
        // use "params" to filter down to the type specified, in this case the "customer" account
        const customerAccount = accounts.filter(account => account.type === params.accountType)
        // return the customerAccount object, which "path" will use to pull the "balance" property
        return customerAccount[0]
      })
  })

  engine.addFact('product', (params, almanac) => {
    // get product list
    return almanac.factValue('products')
      .then(products => {
        // use "params" to filter down to the product specified, in this case the "giftCard" product
        const product = products.filter(product => product.productId === params.productId)
        // return the product object, which "path" will use to pull the "price" property
        return product[0]
      })