xwlee · December 23, 2018 08:04 · Dec 23, 2018
diff --git a/date-directive.js b/date-directive.js
@@ -0,0 +1,78 @@
+const { ApolloServer, gql, SchemaDirectiveVisitor } = require('apollo-server');
+const { GraphQLScalarType, defaultFieldResolver, GraphQLString } = require('graphql');
+const { Kind } = require('graphql/language');
+const formatDate = require("dateformat");
+
+const typeDefs = gql`
+  directive @date(
+    defaultFormat: String = "mmmm d, yyyy"
+  ) on FIELD_DEFINITION
+
+  scalar Date
+
+  type Query {
+    today: Date @date
+  }
+`;
+
+const resolvers = {
+  Query: {
+    today: () => {
+      return new Date;
+    }
+  },
+  Date: new GraphQLScalarType({
+    name: 'Date',
+    description: 'Date custom scalar type',
+    parseValue(value) {
+      return new Date(value); // value from the client
+    },
+    serialize(value) {
+      return value.getTime(); // value sent to the client
+    },
+    parseLiteral(ast) {
+      if (ast.kind === Kind.INT) {
+        return parseInt(ast.value, 10); // ast value is always in string format
+      }
+      return null;
+    },
+  }),
+};
+
+class FormattableDateDirective extends SchemaDirectiveVisitor {
+  visitFieldDefinition(field) {
+    const { resolve = defaultFieldResolver } = field;
+    const { defaultFormat } = this.args;
+
+    field.args.push({
+      name: 'format',
+      type: GraphQLString
+    });
+
+    field.resolve = async function (
+      source,
+      { format, ...otherArgs },
+      context,
+      info
+     ) {
+      const date = await resolve.call(this, source, otherArgs, context, info);
+      // If a format argument was not provided, default to the optional
+      // defaultFormat argument take by the @date directive
+      return formatDate(date, format || defaultFormat);
+    };
+    // The formatted Date becomes a String, so the field type must change:
+    field.type = GraphQLString;
+  }
+}
+
+const server = new ApolloServer({ 
+  typeDefs,
+  resolvers,
+  schemaDirectives: {
+    date: FormattableDateDirective
+  }
+});
+
+server.listen().then(({ url }) => {
+  console.log(`Server ready at ${url}`)
+});