JSFiddle - React, Tailwind, and code Playground

HTML

<input type="radio" id="testa" name="existing" value="no" id="existing-no" onclick="existingPartner('no');"> Existing Yes?

    <input type="radio" id="test" name="existingpartner" value="no" id="existing-no" onclick="existingPartner('no');"> Existing No
    <br><br>

<input type="checkbox" name="mycheckbox" id="mycheckbox" />
<br><br>

<input type="button" id="test-with-prop" value="Test with prop" />

JavaScript

$(document).ready(function(){
    
        var check;   
    
if($("input:radio[name=existingpartner]").is(":checked")){

        // Example 3 - With jQuery prop  
    $("#test-with-prop").on("click", function(){
        check = $("#mycheckbox").prop("checked");
        if(check) {
             alert("Checkbox is checked.");
        } else {
            alert("Checkbox is unchecked.");
        }
    }); 
}

    
    
});