map (mapFn, thisArg) {
    this.data = this.getData().map(mapFn, thisArg)
    return this
  }
Apply a mapping function to the result data.

@example
const JSData = require('js-data');
const { DataStore } = JSData;
console.log('Using JSData v' + JSData.version.full);

const store = new DataStore();
store.defineMapper('user');
const users = [
  { name: 'Peter', age: 25, id: 1 },
  { name: 'Jim', age: 19, id: 2 },
  { name: 'Mike', age: 17, id: 3 },
  { name: 'Alan', age: 29, id: 4 },
  { name: 'Katie', age: 33, id: 5 }
];
store.add('user', users);
const ages = store
  .query('user')
  .map(function (user) {
    return user.age;
  })
  .run();
console.log(ages);

@method Query#map
@param {Function} mapFn Mapping function.
@param {*} [thisArg] Context to which to bind `mapFn`.
@returns {Query} A reference to itself for chaining.
@since 3.0.0