How to use the json-mask.filter function in json-mask

const jsonMask = require('json-mask');
const compile = jsonMask.compile;
const filter = jsonMask.filter;

/**
 * Mask parts of the response.
 *
 *  - `name` querystring param name [fields]
 *
 * @param {Object} opts
 * @return {Promise}
 * @api public
 */

module.exports = opts => {
  opts = opts || {};
  const name = opts.name || 'fields';

  return async function mask(ctx, next) {

var jsonMask = require('json-mask'),
  compile = jsonMask.compile,
  filter = jsonMask.filter;

module.exports = function (opt) {
  opt = opt || {};

  function partialResponse(obj, fields) {
    if (!fields) return obj;
    return filter(obj, compile(fields));
  }

  function wrap(orig) {
    return function (obj) {
      var param = this.req.query[opt.query || 'fields'];
      if (1 === arguments.length) {
        orig(partialResponse(obj, param));
      } else if (2 === arguments.length) {
        if ('number' === typeof arguments[1]) {

const jsonMask = require('json-mask')
const compile = jsonMask.compile
const filter = jsonMask.filter

const defaults = {
  filteringKeyName: 'fields'
}

const getFilterParams = (handler, filteringKeyName) => {
  const { body } = handler.response
  const { queryStringParameters } = handler.event
  const fields = queryStringParameters
    ? queryStringParameters[filteringKeyName]
    : undefined

  return {
    body,
    fields
  }