feat(TypeMapper): allow to override built-in JSON, Date and `Buff…

…er` types

src/TypeMapper.js

@@ -40,6 +40,7 @@ import {
   // isOutputType,
   // isInputType,
   isNamedType,
+  isScalarType,
   valueFromAST,
 } from './graphql';
 import type {
@@ -124,23 +125,26 @@ export class TypeMapper<TContext> {
     ['Int', GraphQLInt],
     ['Boolean', GraphQLBoolean],
     ['ID', GraphQLID],
-    // graphql-compose basic types
-    ['JSON', GraphQLJSON],
-    ['Json', GraphQLJSON],
-    ['Date', GraphQLDate],
-    ['Buffer', GraphQLBuffer],
   ]);
 
   get(name: string): ?GraphQLNamedType {
     const basicScalar = this.basicScalars.get(name);
     if (basicScalar) return basicScalar;
 
     if (!this.schemaComposer.has(name)) {
-      return null;
+      if (name === 'JSON' || name === 'Json') {
+        this.schemaComposer.set(name, GraphQLJSON);
+      } else if (name === 'Date') {
+        this.schemaComposer.set(name, GraphQLDate);
+      } else if (name === 'Buffer') {
+        this.schemaComposer.set(name, GraphQLBuffer);
+      } else {
+        return null;
+      }
     }
 
     const schemaType = this.schemaComposer.get(name);
-    if (isNamedType(schemaType)) {
+    if (isNamedType(schemaType) || isScalarType(schemaType)) {
       return schemaType;
     }
     return schemaType.getType();

src/TypeStorage.js

@@ -4,10 +4,15 @@ import { isFunction } from './utils/is';
 import { TypeComposer } from './TypeComposer';
 import { InputTypeComposer } from './InputTypeComposer';
 import { EnumTypeComposer } from './EnumTypeComposer';
-import type { GraphQLNamedType } from './graphql';
+import type { GraphQLNamedType, GraphQLScalarType } from './graphql';
 
 type K = string;
-type V<TContext> = TypeComposer<TContext> | InputTypeComposer | EnumTypeComposer | GraphQLNamedType;
+type V<TContext> =
+  | TypeComposer<TContext>
+  | InputTypeComposer
+  | EnumTypeComposer
+  | GraphQLNamedType
+  | GraphQLScalarType;
 
 // TypeStorage has all methods from Map class
 export class TypeStorage<TContext> {

src/__tests__/TypeMapper-test.js

@@ -11,6 +11,7 @@ import {
   GraphQLList,
   GraphQLNonNull,
   GraphQLEnumType,
+  GraphQLScalarType,
 } from '../graphql';
 import {
   schemaComposer,
@@ -52,6 +53,29 @@ describe('TypeMapper', () => {
     expect(TypeMapper.get('Buffer')).toBe(GraphQLBuffer);
   });
 
+  it('should allow to override basic graphql-compose types', () => {
+    const CustomJSON = new GraphQLScalarType({
+      name: 'CustomJSON',
+      serialize: () => {},
+    });
+    const CustomDate = new GraphQLScalarType({
+      name: 'CustomDate',
+      serialize: () => {},
+    });
+    const CustomBuffer = new GraphQLScalarType({
+      name: 'CustomBuffer',
+      serialize: () => {},
+    });
+    schemaComposer.set('JSON', CustomJSON);
+    schemaComposer.set('Json', CustomJSON);
+    schemaComposer.set('Date', CustomDate);
+    schemaComposer.set('Buffer', CustomBuffer);
+    expect(TypeMapper.get('JSON')).toBe(CustomJSON);
+    expect(TypeMapper.get('Json')).toBe(CustomJSON);
+    expect(TypeMapper.get('Date')).toBe(CustomDate);
+    expect(TypeMapper.get('Buffer')).toBe(CustomBuffer);
+  });
+
   it('should create object type from template string', () => {
     const type: GraphQLObjectType = (TypeMapper.createType(
       graphqlVersion < 12