Apollo Server Date Directive

date-directive.js

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}`)
});