It might come as a surprise, but yes, you can have input suggestions without using any JavaScript.
<input type="text" list="flavours">
<datalist id="flavours">
<option value="Chocolate"></option>
<option value="Vanilla"></option>
<option value="Strawberry"></option>
<option value="Cherry"></option>
<option value="Watermelon"></option>
<option value="Stracciatella"></option>
</datalist>