How do you concatenate a string with a variable/pass to link?

I'm trying to make a simple page to send IR codes to an app on my phone (OneRemoteToControlThemAll). This is how the dev of the app shows to communicate with it via html, which works 100% fine.

>"Send codes using URI "otrta://code?id=xxx" or "otrta://script?id=xxx" - use it for HTML layouts!"

<button type="button"><a href="otrta://code?id=12372">Left</a></button>

But, this only works with a pre-entered id. So, I want to have a text box with a button that when the button is clicked it sends the code entered in the box. I've looked around for different methods and tried many, none quite working. Here's my most recent attempt:

<script type="text/javascript">
  function myfunction()
  {
    var code = "otrta://code?id=" + document.getElementById("textbox1").value;
    return code;
  }
</script>

html:

<input type="text" name="textbox1" Id="textbox1" style="width: 194px"/>
<button type="button" id="submit"><a href="javascript:myfunction();">Submit</a></button>

Right now on chrome on my PC this takes me to a page and outputs otrta://code?id=1234 or whatever numbers I had entered. On my phone the button does nothing. Any solutions on how to make it act the same as the others and work? It doesn't need to be perfect form, just something that will work, thanks for any help.