Wraps returned JSON array in additional root object with specified key:
SELECT top 3 object_id, name, type FROM sys.objects
FOR JSON PATH, ROOT('data')
Result of the query would be array of JSON objects inside the wrapper object:
{
"data":[
{"object_id":3,"name":"sysrscols","type":"S "},
{"object_id":5,"name":"sysrowsets","type":"S "},
{"object_id":6,"name":"sysclones","type":"S "}
]
}