How do I find all input fields inside a form and copy their values into textarea using Javascript?

I want to add a couple of input fields (name, age, location, status, etc...) to my form.

When I click submit button, how do I get all the values inside a form and place them into a single textarea element, so that it's easy to copy? Thanks for the help!

My current code:

<form>
    <input type="text" id="txt">
    <button type="button" onclick="ShowText();">Submit</button>
</form>
<span id="show"></span>
<script>
    function ShowText(){
        var txt = document.getElementById('txt');
        var show = document.getElementById('show');
        show.innerHTML = txt.value;
    }
</script>