calculate delta of updated row in postgres and notify listener with json

pgv8_trigger.sql

-- Function: tacmon.test_v8()

-- DROP FUNCTION tacmon.test_v8();

CREATE OR REPLACE FUNCTION tacmon.test_v8()
  RETURNS trigger AS
$BODY$// calculate delta
var key, delta = [];
for (key in NEW) {
	var valueOld = OLD[key];
	var valueNew = NEW[key];
	if (valueOld !== valueNew) {
		delta.push([key, valueOld, valueNew]);
	}
}

var info = {
	"table": TG_TABLE_NAME,
	"id": NEW.id,
	"delta:": delta
}

// notify listeners on channel targets
plv8.execute("SELECT pg_notify('targets', $1);", [JSON.stringify(info)] );

// debug message for pgadmin3
// plv8.elog(ERROR, "Delta:", JSON.stringify(info));

return void 0;$BODY$
  LANGUAGE plv8 VOLATILE
  COST 100;
ALTER FUNCTION tacmon.test_v8()
  OWNER TO tacmon;