Reitse Eskens gives it a whirl:
In today’s cloud era, Azure SQL is usually first with new functionality, while on-premises SQL Server follows. One of the new things is the JSON data type and accompanying JSON index.
Because I had to learn how JSON works in SQL Server for my DP-800 exam, I decided to see how the JSON index works and when it works. I’ll go into the execution plans, some details, and check out the statistics when a query runs. Just so you know, this is much deeper than the certification requires, so no need to get this all in your head for the exam.
Click through for a rundown of how this feature works on-premises and what you should be on the lookout for.