How to edit several audio clips into a larger audio clip for download in one audio file (HTML, JS)?

var audio = document.getElementById('mad-libs')
var audio1 = document.getElementById('1')
var audio2 = document.getElementById('2')
var audio3 = document.getElementById('3')
var audio4 = document.getElementById('4')
var audio5 = document.getElementById('5')
var audio6 = document.getElementById('6')
var record = document.getElementById('record')
var mediaRecorder = null
var recording = false
var chunks = []

recordAndStore(audio1)

function recordAndStore (slot) {
  navigator.mediaDevices.getUserMedia({
    audio:true
  }).then(function (stream) {
    mediaRecorder = new MediaRecorder(stream)
    record.addEventListener('click', function (event) {
      if (recording == false) {
        recording = true
        mediaRecorder.start()
        record.textContent = '⏹️ Stop'
      } else {
        recording = false
        mediaRecorder.stop()
        record.textContent = '⏺️ Record'
      }
      mediaRecorder.ondataavailable = function (data) {
        var audioURL = window.URL.createObjectURL(data.data)
        slot.src = audioURL
      }
    })
  }).catch(function (error) {
    console.log(error)
  })
}

audio.hidden {
  display: none;
}
button {
  font-size: 1.35em;
  padding: .25em .5em;
  cursor: pointer;
}

<h1>Mad Libs</h1>
<p>Get Ready To Record Your Mad Libs</p>
<p>Click the record button and say a "noun," "verb," "adjective," or anything else you're prompted for »</p>
<h4 id='prompt'>Common Noun</h4>
<button id="record">⏺️ Record</button>
<audio id="mad-libs" src='audios/mad-libs.m4a' controls class='hidden'></audio>
<audio id='1' controls></audio>
<audio id='2' controls></audio>
<audio id='3' class='hidden'></audio>
<audio id='4' class='hidden'></audio>
<audio id='5' class='hidden'></audio>
<audio id='6' class='hidden'></audio>
<button id="download">Download</button>

<!--

This is the mad libs story...

Once upon a time there was a king with a great big
______ (common noun).

And every morning he took it out on the royal balcony
and ______ (verb, past tense) it for at least 3 hours.

This exhausted the king, and he was very ______
(adjective) to begin with.

The people had gotten very ______ (adjective) with the
king's morning routine.

So they gathered all their ______ (noun, plural),
stormed the castle and ______ (verb, pased tense) the
king.

THE END


-->