filter.js

require([
  'dojo/on',
  'esri/core/Collection',
  'esri/tasks/QueryTask',
  'esri/tasks/support/Query'
], function (on, Collection, QueryTask, Query) {
  var url = 'http://services2.arcgis.com/j80Jz20at6Bi0thr/arcgis/rest/services/Parks/FeatureServer/0';

  var resultsNode = document.getElementById('resultsDiv');
  var input = document.getElementById('autoComplete');

  var qTask = new QueryTask({
    url: url
  });

  var query = new Query({ returnGeometry: false, outFields: ['*'], where: '1=1' });

  var cache = new Collection();
  var collection = new Collection(cache);

  cache.on('change', function () {
    collection.clear();
    collection.addItems(cache);
  });

  collection.on('change', function (e) {
    resultsNode.innerHTML = '';
    collection.map(function (x) {
      var node = document.createElement('li');
      node.setAttribute('class', 'list-group-item');
      node.innerText = x.NAME;
      resultsNode.appendChild(node);
    });
  });

  qTask.execute(query).then(function (results) {
    var attrs = results.features.map(function (x) { return x.attributes; });
    // You could just do new Collection(attrs), but let's
    // demonstrate some change events
    cache.addItems(attrs);
  });

  on(input, 'keyup', function (e) {
    var val = input.value.toLowerCase();
    // filter the cache
    var coll = cache.filter(function (x) {
      return x.NAME.toLowerCase().indexOf(val) > -1;
    });
    collection.clear();
    collection.addItems(coll);
  });

});