postal.js/src/main/DistinctPredicate.js

var DistinctPredicate = function() {
	var previous;
	return function(data) {
		var eq = false;
		if(_.isString(data)) {
			eq = data === previous;
			previous = data;
		}
		else {
			eq = _.isEqual(data, previous);
			previous = _.clone(data);
		}
		return !eq;
	};
};