How to use the graphi.graphql.GraphQLScalarType function in graphi

exports.makeExecutableSchema = ({ typeDefs, resolvers = {} }) => {
  const parsed = graphql.parse(typeDefs);
  const astSchema = graphql.buildASTSchema(parsed, { commentDescriptions: true });

  for (const resolverName of Object.keys(resolvers)) {
    const type = astSchema.getType(resolverName);
    Assert(type || resolverName === '__schema', `Missing schema definition for resolver: ${resolverName}`);

    const typeResolver = resolvers[resolverName];

    // go through field resolvers for the parent resolver type
    for (const fieldName of Object.keys(typeResolver)) {
      const fieldResolver = typeResolver[fieldName];
      Assert(typeof fieldResolver === 'function', `${resolverName}.${fieldName} resolver must be a function`);

      if (type instanceof graphql.GraphQLScalarType) {
        type[fieldName] = fieldResolver;
        continue;
      }

      if (type instanceof graphql.GraphQLEnumType) {
        const fieldType = type.getValue(fieldName);
        Assert(fieldType, `${resolverName}.${fieldName} enum definition missing from schema`);
        fieldType.value = fieldResolver;
        continue;
      }

      // no need to set resolvers unless we are dealing with a type that needs resolvers
      if (!(type instanceof graphql.GraphQLObjectType) && !(type instanceof graphql.GraphQLInterfaceType)) {
        continue;
      }