How to evaluate the date in a rule?

[Ben-CA]

Is there a method to enable the json-rules-engine to determine "if current date is lessThan 2025-06-30"?

I can pass the current date as a fact, but how can I compare a date similar to how you can compare numbers?

[Ben-CA]

Looks like I can just add the current date as a fact:

currentDate: new Date().toISOString().split('T')[0]

And then reference that in my rule as so:

{
  "all": [
    {
      "fact": "currentDate",
      "path": "",
      "value": "2025-01-29",
      "operator": "greaterThan"
    }
  ]
}

Seems to work just fine. :)

Note - there can be some time zone issues with UTC dates, in case anyone is referring to this in the future.

[chris-pardy]

I would highly recommend using the .getTime() method on dates. This returns a number that is irrespective of timezone. If you need to use string representations you should write your own operators to compare dates.

What you have there is not going to work it's going to return false every time since "greaterThan" ensures that the value it got from a fact is a number.

[Ben-CA]

Are you saying then that I'd need to pass the numeric value (seconds since Unix epoch) in the rule AND as the fact?

For the "fact" it doesn't matter, but in the rule, I like them to be human readable if possible.

Or is there a way to make the value in the rule get processed as a date at runtime? (e.g. new Date(rule.value).getTime() - only if the "fact" in the rule === "currentDate")

[chris-pardy]

The only "built-in" way to do this is by having the number in the value field let's assume you don't want to do that here are some other options. Sorted from "worst" to "best"

Custom Fact
A Fact that parses the human readable version from it's params
You need to call engine.addFact before running the rules.
Downside - it's super ugly

  const dateFact = new Fact("date", ({ value }) => new Date(value).getTime());
   ...
  {
  "all": [
    {
      "fact": "currentDate",
      "path": "",
      "value": {
          "fact": "date",
          "params": { "value": "2025-01-29" }
      },
      "operator": "greaterThan"
    }
  ]
}

Custom Operators
Operators that expect a string as one input and turn them into date objects and then do the comparison
You need to call engine.addOperator before running the rules
Downside - you need to build all the comparisons

  const dateLessThan = new Operator('dateGreaterThan', (factValue, value) => factValue > new Date(value).getTime());
  ...
  {
  "all": [
    {
      "fact": "currentDate",
      "path": "",
      "value": "2025-01-29",
      "operator": "dateGreaterThan"
    }
  ]
}

Operator Decorator
An operator decorator that transforms the value into a timestamp
You need to call engine.addOperatorDecorator before running the rules
Downside - a little ugly

  const dateValue = new OperatorDecorator('dateValue', (factValue, value, next) => next(factValue, new Date(value).getTime()));
  ...
  {
  "all": [
    {
      "fact": "currentDate",
      "path": "",
      "value": "2025-01-29",
      "operator": "dateValue:greaterThan"
    }
  ]
}

[Ben-CA]

Thanks for the suggestions; I'll have to decide the route I should take...

[chris-pardy]

Just to clarify the reason I'd prefer the Operator Decorator is that it make all the other operators "just work" so lessThan, greaterThan, lessThanEqual, equal, notEqual
It's also composable so you could have a list of dates and do something like this:

  {
  "all": [
    {
      "fact": "currentDate",
      "path": "",
      "value": [
        "2025-01-29",
        "2024-01-30"
      ],
      "operator": "someValue:dateValue:equals"
    }
  ]
}