Switch GraphQLScalarType methods to callbacks

[IvanGoncharov]

No description provided.

[IvanGoncharov]

At the moment to copy scalar config you should either use type._scalarConfig.serialize or type.serialize.bind(type).
This is a big problem for 3rd-party libraries doing schema transformations.

[mjmahone]

@IvanGoncharov sorry I feel like I'm missing context on this: it seems like an improvement based purely on the fact that the flow types are better, but other than that I am not sure I see why this is desired? The change is straightforward enough I may merge regardless, but wanted to understand your logic.

[IvanGoncharov]

@mjmahone For example, I want to add a prefix to every type in a schema:

function prefixType(type: GraphQLNamedType, prefix: string): GraphQLNamedType {
  if (isScalarType(type)) {
    return new GraphQLScalarType({
      name: prefix + type.name,
      // ...
      parseLiteral: type.parseLiter,
    });
  }
  // ...
}

And parseLiteral: type.parseLiteral is a bug because parseValue, parseLiteral and serialize are method and not a callbacks. And it's very different from all other type-related callbacks like resolve, subscribe, isTypeOf, etc.

Moreover you either need to use private property _scalarConfig or to create wrapper function using bind that would be called every time we graphql-js parses literal. Also if we use bind that mean newly created scalar has refence to old scalar so they can be garbage collected only together.

[IvanGoncharov]

it seems like an improvement based purely on the fact that the flow types are better

@mjmahone This wrapper function depends on this so before proposed change you can't do:

const serialize = GraphQLString.serialize;
serialize(5);
// TypeError: Cannot read property '_scalarConfig' of undefined

Or more complicated scenario:

const newScalar = new GraphQLScalarType({
  name: GraphQLString.name,
  serialize: GraphQLString.serialize,
});
console.log(GraphQLString.serialize(5))
// 5
console.log(newScalar.serialize(5))
// TypeError: Cannot read property '_scalarConfig' of undefined

[mjmahone]

Great, thanks for the context @IvanGoncharov !