Output Ion records as Javascript objects

// IonObjectConverter.ts
import { Reader, IonType, IonTypes } from "ion-js";

/**
 * IonObjectConverter
 * Helper module to take Ion results (QLDB query records) and output Javascript / TS objects for use in 
 * your code / REST API.
 * 
 * See notes here: https://amzn.github.io/ion-docs/guides/cookbook.html#down-converting-to-json
 * and Issue here: https://github.com/amzn/ion-js/issues/531
 * 
 * Usage example:
 *
 *  private resultsToObjects(resultList: Reader[]): Array<IonRecordMap> {
 *   let results: IonRecordMap[] = new Array();
 *    resultList.forEach((reader: Reader) => {
 *      let result: IonRecordMap = convertIonRecord(reader);
 *      results.push(result);
 *    });
 *    return results;
 * }
 *
 */

 export type IonRecordMap = Map<string, any>;

/**
 * convertIonRecord
 * 
 * Pass in an Ion Reader value pointing to a result, and it wil recursively create an Object with the Ion 
 * values.
 *
 * @param reader 
 */
export function convertIonRecord(reader: Reader): any {
    // Assuming at the top level we have a struct, representing the Ion record.
    // The ionly other time we begin this function is when we recurse to a list/sexp/struct
    const result: IonRecordMap = new Map<string,any>();
    reader.next(); // advance from "beginning of structure" to the structure itself
    reader.stepIn(); // enter our structure / list
    let type: IonType | null = null;
    while ((type = reader.next()) !== null) {
        if (reader.fieldName() === null) {
            throw Error("Null field name");
            return undefined;
        }
        const fieldName: string = reader.fieldName()!;
        let value: any = undefined;
        // Do we need to recur?
        if (type.isContainer) {
            reader.stepIn();
            value = convertIonRecord(reader);
            reader.stepOut();
        }
        // If scalar value, fetch it properly
        switch (type) {
            case IonTypes.NULL:
                value = null;
                break;
            case IonTypes.BOOL:
                value = reader.booleanValue();
                break;
            case IonTypes.DECIMAL:
            case IonTypes.FLOAT:
            case IonTypes.INT:
                value = reader.numberValue();
                break;
            case IonTypes.TIMESTAMP:
                break;
            case IonTypes.SYMBOL:
            case IonTypes.STRING:
                value = reader.stringValue();
                break;
            case IonTypes.CLOB:
            case IonTypes.BLOB:
                throw Error("Unhandled Ion type: " + type.name);
                // TODO
                break;
            case IonTypes.LIST:
            case IonTypes.SEXP:
            case IonTypes.STRUCT:
                // Handled above in the recursion function call, do nothing
                break;
            default:
                throw Error("Unhandled Ion type: " + type.name);
        };
        // Set the field we've been looking at in our result structure
        result.set(fieldName, value);
    } // end of while loop on next() - should be end of our structure/list
    reader.stepOut();
    return result;
}