valueAndValidFrom, a helper method for creating a pair of value and validity streams from a single RxJS Observable stream. Rocks the world, at least ours.

jolt-gist.js

function notEmpty(val) {
  return !_.isEmpty(val);
}

function valueAndValidFrom(observable, validator) {
  validator = validator || notEmpty;
  return {
    valueS: observable.filter(validator),
    validS: observable.map(validator)
  };
}



// Usage example 1 with the default validator
// ------------------------------------------

var streetAddress = valueAndValidFrom(
  	$('#user-details-street-address')
			.changeAsObservable()
			.map(byEventTargetValue)
		);

// Subscribe to a value from that stream (triggers only on *valid* values)
streetAddress.valueS.subscribe( fn );

// Subscribe to true/false value about the validity of the stream (triggers on all changes)
streetAddress.validS.subscribe( fn );



// Usage example 2 with a custom validator (validating date picker values)
// -----------------------------------------------------------------------

function validateTravelTime(obj) {
  return obj.start < obj.end;
}

var when = valueAndValidFrom( combinedMappedStreamBasedOn(
    {
      start: startDateS.map(byEventTargetValue),
      end: endDateS.map(byEventTargetValue)
    }
  ), validateTravelTime);



// Usage example 3, validate the combined result of multiple input streams
// -----------------------------------------------------------------------

function allValuesAreTrue(object) {
  var values = _.values(object);
  var and = function (a, b) { return (a && b); };
  return _.reduce(values, and);
}

var everythingIsValidS = combinedMappedStreamBasedOn({
  0: selectedCountry.validS,
  1: when.validS,
  2: reason.validS,
  3: fullname.validS,
  4: streetAddress.validS,
  5: city.validS
}).map(allValuesAreTrue);