Alternative code for Result if 1. it's kept as a class, 2. it's made into an object constructor, or 3 or 4, which are 1 and 2, but slightly rearranged.

1a-class.js

/** 
* All benefit programs' return value should be an instance of this class.
* 
* @todo Implement `.expirationDate` to keep track of data that needs updating
* @todo Figure out how to access this jsdoc definition externally.
* 
* @external
* 
* @class
* @param {object} trial - Data to try out/validate
* @param {string} trial.result - valid values: 'good', 'information', 'warning'
* Proposed valid values: 'good', 'warning', 'bad'. Also, clearer name needed.
* Maybe 'status'.
* @param {string} trial.details - Explanation of results that will be seen
* by the user. Example: 'Your income is x% FPL. Your benefit could go down'.
* Should this be allowed to have a value of `undefined` or `null`?
* @param {string} trial.benefitValue - Monthly subsidy this benefit will provide.
* @param {object} [trial.data] - Any other necessary information.
* @param {object} [trial.expirationDate] - A `Date` object. In future this
* class/object may provide a flag to coders.
*/
class Result {

  constructor ( trial ) {

    let errorMessage = checkTypes( trial );
    /** Check the 2nd line of your error stack to find issue */
    if ( errorMessage.length > 0 ) { throw new Error( errorMessage ) }

    let result = this;
    result.result       = trial.result;
    result.details      = trial.details;
    result.benefitValue = trial.benefitValue;
    result.data         = trial.data;

  }  // End constructor()

};  // End Result class



// ========================================
// ========================================
// (IGNORE) VALIDATION OF RESULT PROPERTIES
// ========================================
// ========================================

/** @todo Add function description */
const checkTypes = function ( data ) {

  /** @todo Is there a way to loop through to do this? I attempted
  * it with a 'types' object to check types, but type tests aren't
  * enough. For example, `expirationDate` needs to be tested for
  * `instanceof Date`. */
  var invalid       = [],
      result        = data.result,
      benefitValue  = data.benefitValue,
      details       = data.details;  // Should this be allowed to be undefined?
    // , date   = data.expirationDate;

  if ( typeof pushUndefined( 'result', result, invalid ) !== 'string' ) {
    if ( typeof result !== 'string' ) {
      invalid.push( 'The value of `result` was type of ' + (typeof result) + ' instead of "string".' );
    }
  }

  if ( typeof pushUndefined( 'details', details, invalid ) !== 'string' ) {
    if ( typeof details !== 'string' ) {
      invalid.push( 'The value of `details` was type of ' + (typeof details) + ' instead of "string".' );
    }
  }

  if ( typeof pushUndefined( 'benefitValue', benefitValue, invalid ) !== 'string' ) {
    if ( typeof benefitValue !== 'number' ) {
      invalid.push( 'The value of `benefitValue` was type of ' + (typeof benefitValue) + ' instead of "number".' );
    }
  }

  // if ( typeof pushUndefined( 'expirationDate', date, invalid ) !== 'string' ) {
  //  if ( !( date instanceof Date ) ) {
  //    invalid.push( 'The value of `expirationDate` was not an instance of `Date`.' );
  //  }
  // }

  var error = invalid.join( ' ' );  // empty array returns a string

  return error;
}


/** @todo Add function description */
const pushUndefined = function ( key, val, invalidArray ) {

  var error = null
  if ( val === undefined ) {
    error = 'The value of `' + key + '` is not allowed to be `undefined`.'
    invalidArray.push( error );
  }

  return error;
};  // End pushUndefined()



// ========================================
// ========================================
// EXPORTS
// ========================================
// ========================================
export { Result }

1b-class.js

/**
* Everything else the same, but declaration of `result` var moved.
* 
* It can be more clear and consistent /in general in a codebase/ if all
* declarations of a `this` holder are always at the very top of the class
* constructor.
*/
class Result {

  constructor ( trial ) {
    let result = this;

    let errorMessage = checkTypes( trial );
    /** Check the 2nd line of your error stack to find issue */
    if ( errorMessage.length > 0 ) { throw new Error( errorMessage ) }

    result.result       = trial.result;
    result.details      = trial.details;
    result.benefitValue = trial.benefitValue;
    result.data         = trial.data;

  }  // End constructor()

};  // End Result class

2a-object.js

/** 
* All benefit programs' return value should be an instance of this object.
* Create with `const myResult = new Result( myValues );`
* 
* @todo Implement `.expirationDate` to keep track of data that needs updating
* @todo Figure out how to access this jsdoc definition externally.
* 
* @external
* 
* @param {object} trial - Data to try out/validate
* @param {string} trial.result - valid values: 'good', 'information', 'warning'
* Proposed valid values: 'good', 'warning', 'bad'. Also, clearer name needed.
* Maybe 'status'.
* @param {string} trial.details - Explanation of results that will be seen
* by the user. Example: 'Your income is x% FPL. Your benefit could go down'.
* Should this be allowed to have a value of `undefined` or `null`?
* @param {string} trial.benefitValue - Monthly subsidy this benefit will provide.
* @param {object} [trial.data] - Any other necessary information.
* @param {object} [trial.expirationDate] - A `Date` object. In future this
* class/object may provide a flag to coders.
*/
const Result = function ( trial ) {

  let errorMessage = checkTypes( trial );
  /** Check the 2nd line of your error stack to find issue */
  if ( errorMessage.length > 0 ) { throw new Error( errorMessage ) }

  let result = {};
  result.result       = trial.result;
  result.details      = trial.details;
  result.benefitValue = trial.benefitValue;
  result.data         = trial.data;

  return result;

};  // End Result {}



// ========================================
// ========================================
// (IGNORE) VALIDATION OF RESULT PROPERTIES
// ========================================
// ========================================

/** @todo Add function description */
const checkTypes = function ( data ) {

  /** @todo Is there a way to loop through to do this? I attempted
  * it with a 'types' object to check types, but type tests aren't
  * enough. For example, `expirationDate` needs to be tested for
  * `instanceof Date`. */
  var invalid       = [],
      result        = data.result,
      benefitValue  = data.benefitValue,
      details       = data.details;  // Should this be allowed to be undefined?
    // , date   = data.expirationDate;

  if ( typeof pushUndefined( 'result', result, invalid ) !== 'string' ) {
    if ( typeof result !== 'string' ) {
      invalid.push( 'The value of `result` was type of ' + (typeof result) + ' instead of "string".' );
    }
  }

  if ( typeof pushUndefined( 'details', details, invalid ) !== 'string' ) {
    if ( typeof details !== 'string' ) {
      invalid.push( 'The value of `details` was type of ' + (typeof details) + ' instead of "string".' );
    }
  }

  if ( typeof pushUndefined( 'benefitValue', benefitValue, invalid ) !== 'string' ) {
    if ( typeof benefitValue !== 'number' ) {
      invalid.push( 'The value of `benefitValue` was type of ' + (typeof benefitValue) + ' instead of "number".' );
    }
  }

  // if ( typeof pushUndefined( 'expirationDate', date, invalid ) !== 'string' ) {
  //  if ( !( date instanceof Date ) ) {
  //    invalid.push( 'The value of `expirationDate` was not an instance of `Date`.' );
  //  }
  // }

  var error = invalid.join( ' ' );  // empty array returns a string

  return error;
}


/** @todo Add function description */
var pushUndefined = function ( key, val, invalidArray ) {

  var error = null
  if ( val === undefined ) {
    error = 'The value of `' + key + '` is not allowed to be `undefined`.'
    invalidArray.push( error );
  }

  return error;
};  // End pushUndefined()



// ========================================
// ========================================
// EXPORTS
// ========================================
// ========================================
export { Result }

2b-object.js

/**
* Everything else the same, but declaration of `result` var moved.
* 
* It can be more clear and consistent /in general in a codebase/ if all
* declarations of the returned object are always at the very top of the
* object constructor.
*/
const Result = function ( trial ) {
  let result = {};

  let errorMessage = checkTypes( trial );
  /** Check the 2nd line of your error stack to find issue */
  if ( errorMessage.length > 0 ) { throw new Error( errorMessage ) }

  result.result       = trial.result;
  result.details      = trial.details;
  result.benefitValue = trial.benefitValue;
  result.data         = trial.data;

  return result;

};  // End Result {}