How to check radio button is checked using JQuery?

jQuery 3.3.1

if (typeof $("input[name='yourRadioName']:checked").val() === "undefined") {
    alert('is not selected');
}else{
    alert('is selected');
}

//the following code checks if your radio button having name like 'yourRadioName' 
//is checked or not
$(document).ready(function() {
  if($("input:radio[name='yourRadioName']").is(":checked")) {
      //its checked
  }
});

Given a group of radio buttons:

<input type="radio" id="radio1" name="radioGroup" value="1">
<input type="radio" id="radio2" name="radioGroup" value="2">

You can test whether a specific one is checked using jQuery as follows:

if ($("#radio1").prop("checked")) {
   // do something
}

// OR
if ($("#radio1").is(":checked")) {
   // do something
}

// OR if you don't have ids set you can go by group name and value
// (basically you need a selector that lets you specify the particular input)
if ($("input[name='radioGroup'][value='1']").prop("checked"))

You can get the value of the currently checked one in the group as follows:

$("input[name='radioGroup']:checked").val()