SQL Server 2016 for JSON output integer array

Question

I'd like to get JSON with an array of integers using SQL Server 2016's For JSON feature. I'm stumped on array of integers.

Database table structures:

declare @Employees table (ID int, Name nvarchar(50))
insert into @Employees values
(1, 'Bob'),
(2, 'Randy')

declare @Permissions table (ID int, PermissionName nvarchar(50))
insert into @Permissions values
(1, 'Post'),
(2, 'Comment'),
(3, 'Edit'),
(4, 'Delete')

declare @EmployeePermissions table (EmployeeID int, PermissionID int)
insert into @EmployeePermissions values
(1, 1),
(1, 2),
(2, 1),
(2, 2),
(2, 3)

Desired results:

{"EmployeePermissions": [
  {"Employee":"Bob", "Permissions":[1,2]},
  {"Employee":"Randy", "Permissions":[1,2,3]}
]}

This is the closest I've gotten, but not quite what I want.

select
    e.Name as Employee,
    (select 
         convert(nvarchar(10),ep.PermissionID) as PermID 
     from @EmployeePermissions ep 
     where ep.EmployeeID=e.ID 
     for json path) as 'Permissions'
from
    @Employees e
for json path, root('EmployeePermissions')

returns:

{"EmployeePermissions": [
  {"Employee":"Bob", "Permissions":[{"permID":1},{"permID":2}]},
  {"Employee":"Randy", "Permissions":[{"permID":1},{"permID":2},{"permID":3}]}
]}

SOLUTION - SQL Server 2017 and on

select
    e.Name as Employee,
    (select 
         '[' + STRING_AGG(ep.PermissionID, ',') + ']' 
     from @EmployeePermissions ep 
     where ep.EmployeeID=e.ID) as Permissions 
from
    @Employees e
for json path, root('EmployeePermissions')

Answer 1

This should work on SQL Server 2017 (14.x) and later

SELECT '[' + STRING_AGG(ep.PermissionID, ',') + ']'
FROM @EmployeePermissions ep

You have to cast your value to NVarchar(max) only if your result string exceed 8000bytes

SELECT '[' + STRING_AGG(cast(ep.PermissionID AS NVARCHAR(MAX)), ',') + ']'
FROM @EmployeePermissions ep

FullQuery

SELECT e.Name as Employee,
    (SELECT 
         '[' + STRING_AGG(cast(ep.PermissionID AS NVARCHAR(MAX)), ',') + ']' 
     FROM @EmployeePermissions ep 
     WHERE ep.EmployeeID=e.ID) as Permissions 
FROM
    @Employees e
FOR JSON PATH, root('EmployeePermissions')