函数构造函数对象与对象内部对象之间的javascript区别

Question

I am trying to comprehend/understand GraphQL schema instructor have used.

So first he did something like this

const BookType = new GraphQLObjectType({  
    name: 'Book', 

    fields: () => ({
        id: { type: GraphQLString},
        name: { type: GraphQLString},
        genre: { type: GraphQLString }
    })
})

Here, he mentioned that reason fields needs to be a function is because later when we have multiple type and they have reference to one another. then unless we wrap it in function, one type won't know what other types (more later)

And afterwards when he was making RootQuery he did something like this

const RootQuery = new GraphQLObjectType({
    name: "RootQueryType",
    fields: {
        book: {
          type: BookType, 
          args: { id: { type: GraphQLString }},
          resolve(parent, args){
           args.id
            }
         }
      }
})

Here, he did fields: { instead of fields: () => ({ for which he gave following reason

We don't need to wrap it like the field above because we don't need to worry about the order so much inside root Query

[Question:] I am unable to understand his explanation so I was looking for someone to explain me why he did fields: { instead of fields: () => ({ this?

Answer 1

This is probably because inside your RootQueryType, the field book does not contain any reference of any of your custom declared types let's say AuthorType. Your field book is therefore, only dependant on either BookType or any of the other GraphQLObjects that you may have imported at the top. Same goes for the field author. There should not be any reference of BookType inside it.

However, in the case of your custom Types( BookType or AuthorType), they might contain references of each other and hence they are dependant on each other.

Therefore when defining those custom types, your fields needs to be wrapped inside function. But that's not a necessity when it comes to the RootQuery.

If you want to know more about it. Look up the concept of Hoisting.