how to show selected value in php dropdown after submit code example

Example: php get selected value from dropdown without submit

<select id="singleSelectValueDDJS" class="form-control"
                    onchange="singleSelectChangeValue()">
  <option value="0">Select Value 0</option>
  <option value="8">Option value 8</option>
  <option value="5">Option value 5</option>
  <option value="4">Option value 4</option>
</select>

<input type="text" id="textFieldValueJS" class="form-control"
                    placeholder="get value on option select">Copy