Norwegian is complicated and doesn't function like a traditional legacy airline. In addition to operating as an European continental low-cost carrier, they're also a long-haul low-cost carrier that bears more resemblance to Jetstar or Air Asia X with a la carte service on long-thin routes using modern equipment and high-density cabins.
To complicate things further, Norwegian utilizes
four air operating certificates (two in Norway, one in the UK, and one in Ireland). The US currently only allows service using one of the Norwegian air operating certificate entities, but Norwegian can still share planes within the entire group and operate flights to the US from bases spread across Europe. Norwegian currently operates flights with 787 equipment to LAX, JFK, Boston, Orlando, Ft. Lauderdale, San Juan Puerto Rico, and St. Croix US Virgin Islands flying from Oslo, Stockholm, Copenhagen, Paris, and London Gatwick.
Here's a good interview with the president of Norwegian, who seems like a rambunctious and pugilistic character, which are traits appropriate for an executive taking on incumbent legacy carriers.
https://skift.com/2016/10/06/norwegian-air-ceo-interview-regulators-and-airlines-are-afraid-of-us/
Norwegian also intends to operate transatlantic service with B737Max-8 aircraft when those join their fleet, and is building up a long-haul base in Barcelona.