javascript press key function

I want to add my javascript a key press function because my script run automaticaly

I want it when i press a specific key it will run and stop

The JS will not run / run automaticaly until i press "a"

When I press "a" it will run;

When I press "e" it will stop.

Can you add it to my javascript, Thanks.

here is the code bellow:

var currentpos = 0,
  alt = 1,
  curpos1 = 0,
  curpos2 = -1

function initialize() {
  startit()
}

function scrollwindow() {
  if (document.all)
    temp = document.body.scrollTop
  else
    temp = window.pageYOffset
  if (alt == 0)
    alt = 1
  else
    alt = 0
  if (alt == 0)
    curpos1 = temp
  else
    curpos2 = temp
  if (curpos1 != curpos2) {
    if (document.all)
      currentpos = document.body.scrollTop + 1
    else
      currentpos = window.pageYOffset + 1
    window.scroll(0, currentpos)
  } else {
    currentpos = 0
    window.scroll(0, currentpos)
  }
}

function startit() {
  setInterval("scrollwindow()", 10) // change the value for speed the bigger the slow
}

window.onload = initialize

<header id="top"></header>
<main>
  <article>
    <!-- long form content here -->
  </article>
  <br>
  <h1 id="chapter-heading">My Plug-in Spirit Ring</h1>
  </br>
  <div class=mp3>
    <audio controls autoplay loop>
        <source src="bg.mp3" type="audio/mpeg">
    </audio>
  </div>
  <div style="font-size:0; position: absolute; left: 20%; top: 10%">
    <img src="Cover.png" />
    <img src="1.png" />
    <img src="2.png" />
    <img src="3.png" />
    <img src="4.png" />
    <img src="Thanks.gif" />
  </div>
</main>

Thank you!

Via Active questions tagged javascript - Stack Overflow https://ift.tt/qfys7Th