JSFiddle - React, Tailwind, and code Playground

HTML

<form name="results" action="request_job.php" method="post" onsubmit="return validate();">
<input type='checkbox' name='ModelArray[]' value='1'>m1
<input type='checkbox' name='ModelArray[]' value='2'>m2
<input type='checkbox' name='ModelArray[]' value='3'>m3
<input type='checkbox' name='ModelArray[]' value='4'>m4
<input type='checkbox' name='ModelArray[]' value='5'>m5
<input type='checkbox' name='ModelArray[]' value='6'>m6
<input type='checkbox' name='ModelArray[]' value='7'>m7
<input type="submit" value="submit">
</form>

JavaScript

function validate() {
    var i, chks = document.getElementsByName('ModelArray[]');
    for (i = 0; i < chks.length; i++)
        if (chks[i].checked)
            return true;
    alert('nothing selected');
    return false;
}