JSFiddle - React, Tailwind, and code Playground

HTML

<form action="" method="post">
first Name:<input type="text" name="first_name"/> <br/>
last name:<input type="text" name="last_name"/> <br/>
Widget URL:<input type="text" name="zip"/> <br/>

Support:<br/>
span3:<input type="checkbox" name="subjects" value="bee"/><br/>
span6:<input type="checkbox" name="subjects" value="ms"/><br/>
span12:<input type="checkbox" name="subjects" value="edc"/><br/>

<p><input type="button" id="btnsubmit" value="submit"/></p>
</form>
<pre id="json_output"></pre>

JavaScript

$(document).ready(function(){
    
    var formObject = {};
    
    $('#btnsubmit').click(function(){
        
       var formInputString = $('form').serialize();
       var inputParameters = formInputString.split('&');
       var nameValues = [];
        $.each(inputParameters,function(i){
            var inputParameter = inputParameters[i].split('='); // 0 - keyName , 1 - keyValue
            var keyName = inputParameter[0];
            var keyValue = inputParameter[1];
            if(keyName == 'subjects'){
                nameValues.push({ name : keyValue});
                formObject[keyName] = nameValues;
            }else{
                formObject[keyName] = keyValue;
            }

        });
        
        var myString = JSON.stringify(formObject);
        
        $('#json_output').text(myString);
    });
    
});