MongooseJS - how to define a custom type

Question

Using "mongoose": "4.9.8", I want to define a type for consistency and reuse. I know the concept, but I'm a little stuck on the syntax, For instance, say my mongoose schema looks like this

const thingsSchema = new Schema({
    thing: {
        type: String
        ,required: false
    }   
    ,location: {
        city: {
            type: String
            ,required: false
        }
        ,state: {
            type: String
            ,required: false
        }
        ,country: {
            type: String
            ,required: false
        }
    }   
});

what I really want to do is use "Location" model/type over again elsewhere, and have location not be required...like this:

const thingsSchema = new Schema({
    thing: {
        type: String
        ,required: false
    }   
    ,location: {
        type: Location
        ,required: false
    }   
});

I think it's done something like this - but Im unsure.

const Location: {
        city: {
            type: String
            ,required: false
        }
        ,state: {
            type: String
            ,required: false
        }
        ,country: {
            type: String
            ,required: false
        }
    };