JSFiddle - React, Tailwind, and code Playground

by Town

HTML

<input type='checkbox' name='power_convention[]'  value='SOME VALUE #1' />
<input type='checkbox' name='power_evidence[]' value='SOME VALUE #2' />

<textarea id="elm1" name="comments" rows="15" cols="80" style="width: 80%"></textarea>

JavaScript

$('input[name^="power_"]').click(function() {
    // assuming you only want the value if the checkbox is being ticked
    // not when it's being unticked
    if ($(this).is(":checked")) {
        
        // to overwrite
        $('#elm1').val("<h3>" + this.value + "</h3><br />");
        
        // to append
        //$('#elm1').val(
        //    $('#elm1').val() + "<h3>" + this.value + "</h3><br />"
        //);
    }
});