https://graphql.org/learn/pagination implementation

PaginateDirective.js

"use strict";

/**
 * directive @paginate on FIELD_DEFINITION
 * """
 * abstract type Page {
 *   totalCount: Int!
 *   edges: [Edge!]!
 *   pageInfo: PageInfo!
 * }
 * abstract type Edge {
 *   node: Node!
 *   cursor: ID!
 * }
 * abstract type PageInfo {
 *   endCursor: ID
 *   hasNextPage: Boolean!
 * }
 * """
 */

const {
  defaultFieldResolver,
  GraphQLBoolean,
  GraphQLID,
  GraphQLInt,
  GraphQLList,
  GraphQLNonNull,
  GraphQLObjectType
} = require("graphql");
const {SchemaDirectiveVisitor} = require("apollo-server-express");

const PageInfoType = new GraphQLObjectType({
  name: "PageInfo",
  fields: {
    endCursor: {type: GraphQLID},
    hasNextPage: {type: new GraphQLNonNull(GraphQLBoolean)}
  }
});

function createPaginatedType(field) {
  const EdgeType = new GraphQLObjectType({
    name: `${field.name}Edge`,
    fields: {
      node: {type: new GraphQLNonNull(field.type)},
      cursor: {type: new GraphQLNonNull(GraphQLID)}
    }
  });
  return new GraphQLObjectType({
    name: `${field.name}Page`,
    fields: {
      totalCount: {type: new GraphQLNonNull(GraphQLInt)},
      edges: {
        type: new GraphQLNonNull(
          new GraphQLList(
            new GraphQLNonNull(EdgeType)
          )
        )
      },
      pageInfo: {type: new GraphQLNonNull(PageInfoType)}
    }
  });
}

class PaginateDirective extends SchemaDirectiveVisitor {
  visitFieldDefinition(field) {
    const {resolve = defaultFieldResolver} = field;
    Object.assign(field, {
      async resolve(...args) {
        return await resolve.apply(this, args);
      },
      type: createPaginatedType(field)
    });
  }
}

module.exports = PaginateDirective;