feat: defining a custom scalar DateTime

src/resolvers.js

@@ -1,5 +1,6 @@
 const { UserInputError } = require('apollo-server');
 const yup = require('yup');
+const dateTimeScalar = require('./scalars/dateTime');
 const data = require('./data');
 
 const uuidSchema = yup.string().min(36).max(36);
@@ -76,5 +77,6 @@ module.exports = {
       const { reservationProducts } = input;
       return data.createReservation({ reservationProducts });
     }
-  }
+  },
+  DateTime: dateTimeScalar,
 };

src/scalars/dateTime.js

@@ -0,0 +1,65 @@
+const { GraphQLScalarType } = require('graphql');
+const { GraphQLError } = require('graphql/error')
+const { Kind } = require('graphql/language');
+
+module.exports = new GraphQLScalarType({
+  name: 'DateTime',
+  description: 'Use JavaScript Date object for date/time fields.',
+  serialize(value) {
+    let v = value;
+
+    if (!(v instanceof Date) && typeof v !== 'string' && typeof v !== 'number') {
+      throw new TypeError(
+        `Value is not an instance of Date, Date string or number: ${v}`,
+      );
+    }
+
+    if (typeof v === 'string') {
+      v = new Date();
+
+      v.setTime(Date.parse(value));
+    } else if (typeof v === 'number') {
+      v = new Date(v);
+    }
+
+    if (Number.isNaN(v.getTime())) {
+      throw new TypeError(`Value is not a valid Date: ${v}`);
+    }
+
+    return v.toJSON();
+  },
+
+  parseValue(value) {
+    const date = new Date(value);
+
+    if (Number.isNaN(date.getTime())) {
+      throw new TypeError(`Value is not a valid Date: ${value}`);
+    }
+
+    return date;
+  },
+
+  parseLiteral(ast) {
+    if (ast.kind !== Kind.STRING && ast.kind !== Kind.INT) {
+      throw new GraphQLError(
+        `Can only parse strings & integers to dates but got a: ${ast.kind}`,
+      );
+    }
+
+    const result = new Date(ast.kind === Kind.INT ? Number(ast.value) : ast.value);
+
+    if (Number.isNaN(result.getTime())) {
+      throw new GraphQLError(`Value is not a valid Date: ${ast.value}`);
+    }
+
+    if (ast.kind === Kind.STRING && ast.value !== result.toJSON()) {
+      throw new GraphQLError(
+        `Value is not a valid Date format (YYYY-MM-DDTHH:MM:SS.SSSZ): ${
+          ast.value
+        }`,
+      );
+    }
+
+    return result;
+  },
+});

src/typeDefs.js

@@ -3,11 +3,13 @@ const { gql } = require('apollo-server');
 // Type definitions define the "shape" of your data and specify
 // which ways the data can be fetched from the GraphQL server.
 module.exports = gql`
+  scalar DateTime
+
   # Comments in GraphQL are defined with the hash (#) symbol.
 
   type Product {
     description: String
-    id: String
+    id: ID
     name: String
     price: Float
   }
@@ -15,7 +17,7 @@ module.exports = gql`
   # This "Store" type can be used in other type declarations.
   type Store {
     city: String
-    id: String
+    id: ID
     name: String
     number: Int
     postalCode: String
@@ -29,8 +31,8 @@ module.exports = gql`
   }
 
   type Reservation {
-    date: String
+    date: DateTime
-    id: String
+    id: ID
     reservationProducts: [ReservationProduct]
   }
 
@@ -38,7 +40,7 @@ module.exports = gql`
   # (A "Mutation" type will be covered later on.)
   type Query {
     stores: [Store]
-    store(id: String): Store
+    store(id: ID): Store
   }
 
   input StoreInput {