fact params is not working when I am using fact in evaluationDetails > currentValue #424

Activity

1. AayushOjha commented on Jul 13, 2026

   

   AayushOjha

   on Jul 13, 2026

   More actions

   Hi @dlsemwal, I looked into this and was able to reproduce the issue. It behaves a little differently from what was originally described though.

   What's actually happening: Fact references inside nested event.params are never resolved, regardless of whether they have params or not. The params: {} you saw in your resolver was most likely coming from another place (for example, the rule conditions), not from currentValue.

   Minimal repro (v7.3.2, replaceFactsInEventParams: true):

   const { Engine } = require('json-rules-engine')
   
   const engine = new Engine([], { replaceFactsInEventParams: true })
   
   engine.addFact('documentsCount', (params) => {
     console.log('resolver params:', params)
     return 3
   })
   engine.addFact('stdDocCount', () => 5)
   
   engine.addRule({
     conditions: {
       all: [{ fact: 'documentsCount', params: { status: 'approved' }, operator: 'greaterThanInclusive', value: { fact: 'stdDocCount' } }]
     },
     event: {
       type: 'RuleEventErrorCode',
       params: {
         // top-level fact reference — resolved correctly, params reach the resolver ✓
         topLevelCount: { fact: 'documentsCount', params: { status: 'approved' } },
         // nested fact reference (as in this issue) — returned as-is, never resolved ✗
         evaluationDetails: {
           currentValue: { fact: 'documentsCount', params: { status: 'approved' } },
           targetValue: { fact: 'stdDocCount' }
         }
       }
     }
   })
   
   engine.run().then(({ failureEvents }) => console.dir(failureEvents[0].params, { depth: null }))

   Output:

   {
     topLevelCount: 3,                                    // resolved
     evaluationDetails: {
       currentValue: { fact: 'documentsCount', params: { status: 'approved' } },  // untouched
       targetValue: { fact: 'stdDocCount' }               // untouched
     }
   }

   Root cause: RuleResult.resolveEventParams (src/rule-result.js#L18) only loops over the top-level properties in event.params. almanac.getValue already handles params correctly, but it's only called for top-level values. So if a { fact: ... } reference is nested deeper, it never gets resolved.

   Proposed fix: Update resolveEventParams to walk through event.params recursively. It would traverse plain objects and arrays, and whenever it finds a { fact: ... } object, it resolves it and stops traversing that branch (so the fact's own params stay untouched). This doesn't require a new API, stays behind the existing replaceFactsInEventParams flag, and doesn't change the current top-level behaviour.

   The only possible behaviour change is for anyone who was intentionally relying on nested { fact: ... } objects being left untouched when this flag is enabled. If that's a concern, we could introduce a separate opt-in (something like replaceFactsInEventParams: 'deep'). Personally, I think recursive resolution matches what this flag was always expected to do.

   @chris-pardy does that sound reasonable? If so, I'm happy to open a PR with the fix and add a test case based on the example from this issue.