Writing some js for an html file where i input a sentence (string). and when i click a button, it outputs the amount of each individual vowel, excluding y and not paying attention to punctuation. I cannot use var so i am trying to make this work using let. I believe i'm on the right path here,starting with the vowel a, yet if the sentence doesn't contain an a i get an error. I can't think of what to do next. Any thoughts?

```js
'use strict';

let vButton = document.querySelectorAll('#vowels');
vButton.forEach(function(blip) {
  blip.addEventListener('click', function(evt) {
    evt.preventDefault();
    console.log('click');

    let vowelString = document.getElementById('roboInput'),
      sentence = vowelString.value;
    if (sentence !== '') {
      let aMatches = sentence.match(/a/gi).length;
      alert("a - " + aMatches);
    }
    vowelString.value = '';

  });
});
```

```css
a {
  cursor: pointer;
}

.well-robot {
  min-height: 340px;
}

.input-robot {
  width: 100%;
  min-height: 100px;
}

.output-robot {
  border: 1px solid #000000;
  min-height: 150px;
  margin-top: 10px;
}
```

```html
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap-theme.min.css">
<div class="container">
  <div class="alert alert-info">
    Hello! I'm a smart robot. I can do many interesting things. Type something below and click a button to watch me work!
  </div>
  <div class="row">
    <div class="col-sm-4">
      <img src="./robot.gif">
    </div>
    <div class="col-sm-8 well well-robot">
      <textarea id="roboInput" placeholder="Input something here!" class="input-robot"></textarea>
      <div class="btn-group btn-group-justified">
        <a class="btn btn-default" id="vowels">Count Vowels</a>
        <a class="btn btn-default" id="anagrams">Count Anagrams</a>
        <a class="btn btn-default" id="distance">Word Distance</a>
      </div>
      <div id="robotResult" class="output-robot">
      </div>
    </div>
  </div>
</div>
```