I've made a little web-application. And want to make when I push 'enter' there must be check if there is empty or space value. In this case I have 'alert'.

So I used event listener. But it works incorrect. Alert appears when I push not only 'enter'. Need your help!

```js
const convert = document.getElementById('convert');

currentValue.addEventListener('keypress', function(event) {
  if (event.which === 13 && currentValue.value === '' ||
    currentValue.value === ' ') {
    alert('value is empty');
  } else {
    convertTemperature();
  }
}, false);
```

```html
<div id="application">
  <input id="currentValue" type="number">
  <select id="select">
    <option value="celsius">Celsius</option>
    <option value="fahrenheit">Fahrenheit</option>
    <option value="kelvin">Kelvin</option>
  </select>
  </br>
  <button id="convert">Convert</button>
  </br>
  <input id="value1" type="text">
  </br>
  <input id="value2" type="text">
</div>
```