JSFiddle - React, Tailwind, and code Playground

HTML

<div id="combined">
</div>
    
<input type="text" value="a" class="output" />
<input type="text" value="b" class="output" />
<input type="text" value="c" class="output" />

JavaScript

function doCombine() {
    var combined = document.getElementById('combined');
    var outputs = document.getElementsByClassName('output');
    
    for(var i=0; i<outputs.length; i++){
        combined.innerHTML += outputs[i].value + ',';
    }
}

doCombine();