JSFiddle - React, Tailwind, and code Playground

HTML

Please select at least one Checkbox
<br>
<br>
<form name = "FC" id = "myForm">
<input type = "checkbox" class='myCheckBox' name = "c1" value = "c1"> C1 <br>
<input type = "checkbox" class='myCheckBox'name = "c1" value = "c2"> C2 <br>
<input type = "checkbox" class='myCheckBox' name = "c1" value = "c3"> C3 <br>
<input type = "checkbox" class='myCheckBox' name = "c1" value = "c4"> C4 <br>
</form>
<br>
<br>
<input type = "button" value = "Edit and Report" onClick="valthis()">

JavaScript

function valthis() {
var checkBoxes = document.getElementsByClassName( 'myCheckBox' );
var isChecked = false;
    for (var i = 0; i < checkBoxes.length; i++) {
        if ( checkBoxes[i].checked ) {
            isChecked = true;
        };
    };
    if ( isChecked ) {
        alert( 'At least one checkbox checked!' );
        } else {
            alert( 'Please, check at least one checkbox!' );
        }   
}