Create custom validation rule

Here's how you would implement a validator that checks if a value is between to numbers

function validator_factory(min, max) {
  return {
    refs: [], // this is used if the validator
    params: {
      min,
      max
    },
    validate: function(value, path, context) {
      // the value is not required so if it's falsy we return true
      if (!value) {
        return true;
      }

      return value >= this.params.min && value <= this.params.max
    }
  }
}
SiriusValidation.add_rule('custom_rule', validator_factory, 'This field should be between {min} and {max}');

To recap:

1. You need a validator factory that returns an object that has to have at least the validate() method
2. params property holds the values that the validator depends on
3. refs property holds a list of referenced paths. This is required when you need contextual validation so that some elements are re-validated when the referenced paths change.

In the example above min and max are assumed to be numbers but they could be references to other elements in the form. In this case the refs property should be populated accordingly. This is how we did it for the equal built-in rule.

The validate() method should return a boolean OR a promise that returns a boolean, for async validators