GraphQL Paginated Query Implementation

schema.ts

units: {
      type: pagination.Page(Unit),
      description: "Return the 'first' X number of items 'after' the specified cursor'",
      args: {
        first: {
          type: graphql.GraphQLInt,
          description: "Limits the number of results returned in the page. Defaults to 10."
        },
        after: {
          type: graphql.GraphQLString,
          description: "The cursor value of an item returned in previous page. An alternative to in integer offset."
        }
      },
      resolve: function (root: any, { first = 10, after } : { first: number, after: string }) {
        let afterIndex: number = 0;

        // Get ID from after argument or default to first item.
        if (typeof after === "string") {
          let  id = pagination.convertCursorToNodeId(after);
          if (typeof id === "number") {
            const matchingIndex = utilities.findIndex(unit => unit.id === id, balanceData.units);
            if (matchingIndex != -1) {
              afterIndex = matchingIndex;
            }
          }
        }

        // Add 1 to exclude item matching after index.
        const sliceIndex = afterIndex + 1;

        const edges = balanceData.units
          .slice(sliceIndex, sliceIndex + first)
          .map(node => ({
              node,
              cursor: pagination.convertNodeToCursor(node)
          }));

        const startCursor = edges.length > 0 ? pagination.convertNodeToCursor(edges[0].node) : null;
        const endCursor = edges.length > 0 ? pagination.convertNodeToCursor(edges[edges.length-1].node) : null;
        const hasNextPage = balanceData.units.length > sliceIndex + first;

        return {
          totalCount: balanceData.units.length,
          edges,
          pageInfo: {
            startCursor,
            endCursor,
            hasNextPage
          }
        };
      }
    }