Using nashorn, array.splice(1) means array.splice(1, 0), this is the standard behavior but it is not compliant with v8.
Using v8, array.splice(1) means array.splice(1, rooms.length); This is a non standard behavior but is the defacto standard defined by: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/splice