Javascript - Typeahead.

npm install getaddress-typeahead

<script src="https://cdn.getaddress.io/scripts/getaddress-typeahead-1.1.0.min.js"></script>

  <label for="textbox_postcode" class="control-label">Postcode:</label>
  <input type="text" id="textbox_postcode" > 


  <script>
    getAddress.typeahead("textbox_postcode","postcode", "API Key or Domain Token");
  </script>

The full list of options, and their defaults:

getAddress.typeahead(
        'textbox_id',
         search_on: 'postcode|locality|town_or_city|district|county|country', /*the field to search on*/
        'API KEY or Domain Token'
        }
    );