Animated output based on single input field

Question

I'm trying to animate an output which is calculated based on a single input value * 4.5. The calculation itself is working but I cannot figure out how to animate the value, what I'm trying to do is have the output count up to the calculated value quite quickly. I've found https://codepen.io/shivasurya/pen/FatiB which has the count animation I'd like to implement, but can't figure out how to implement it to my input and output fields, so far I have:

<form id="ewcalc" oninput="updateOutput()"> 
<input name="income" type="number" value="0" />
<output for="income" name="loan">0</output>
</form>

<script type="text/javascript">
function updateOutput() {
var form = document.getElementById("ewcalc");

form.elements["loan"].value=eval(parseInt(form.elements["income"].value) * 4.5);
}
</script>

Any suggestions how I can implement the animation? I've tried several things, none of which are working, and getting errors if I try using onsubmit.

Answer 1

You'll probably want to use requestAnimationFrame like this:

function updateOutput() {
  var income = $("#income").val() * 4.5;
  var output = Number($("#loan").text());

  if (income !== output) {
    if (income > output)
      output += 0.5;
    else if (income < output)
      output -= 0.5;

    $("#loan").text(output);
    requestAnimationFrame(updateOutput);
  }
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<form id="ewcalc" oninput="updateOutput()">
  <input id="income" type="number" value="0" />
  <output for="income" id="loan">0</output>
</form>