Choosing between using type vs interface is about the constraints in the features for each. With 3.7, one of the constrains on type but not in interface was removed. You can find out more about this in example:types-vs-interfaces It used to be that you could not refer to the type you are defining inside the type itself. This was a limit which didn't exist inside an interface, and could be worked around with a little work. For example, this is not feasible in 3.6:

type ValueOrArray = T | Array>;

type ValueOrArray2 = T | ArrayOfValueOrArray;
interface ArrayOfValueOrArray extends Array> { }

type Json = string | number | boolean | null | Json[] | { [key: string]: Json };

const exampleStatusJSON: Json = {
  available: true,
  username: "Jean-loup",
  room: {
    name: "Highcrest",
    // Cannot add functions into the Json type
    // update: () => {}
  },
};