How do I get the value from my checkbox and save it in my database?

Question

Basically, what I want to do is to add contacts as favourites. I list contacts out with checkboxes and send the value back to my database after checking the checkboxes. How do I get value from the checked checkboxes to be saved in my database?

function mycontacts(){
         var xmlhttp = new XMLHttpRequest();
         var url = serverURL() + "/listcontact.php";
         url += "?phoneno=" + localStorage.getItem("phoneno") +
         "&contactno=" + contactno + "&contactid" + contactid;

         xmlhttp.onreadystatechange=function() {
         if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
         getContacts(xmlhttp.responseText);
         }
         }
         xmlhttp.open("GET", url, true);
         xmlhttp.send();
         }

function getContacts(response) {
        var arr = JSON.parse(response);
        var tbl=$("<table/>").attr("id","mytable");
        $("#div1").append(tbl);
        for(var i=0;i<arr.length;i++){  
        var tr="<tr>";
        var chk="<th>"+"<input type='checkbox' />"+"</th>";
        var td1="<td>"+arr[i].contactname+"</td>";
        var td2="<td>"+arr[i].contactno+"</td></tr>";
        $("#mytable").append(tr+chk+td1+td2); 
        }
    }

function savefavourite(){
        contactName =  $("#contactname").val();
        contactno = $("#contactno").val(); 
        phoneno = localStorage.getItem("phoneno");

        if (validate()){ 
            var xmlhttp = new XMLHttpRequest(); 
            var url = serverURL() + "/favourite.php";
            url += "?contactName=" + contactName + "&contactno=" + contactno + "&phoneno=" + phoneno;
            xmlhttp.onreadystatechange=function() { 
                 if (xmlhttp.readyState == 4 && xmlhttp.status == 200) { 
                     getFavourite(xmlhttp.responseText); 
                 }
            }
            xmlhttp.open("GET", url, true);
            xmlhttp.send();             
        }
    }

    function validate(){
        var validate = true; 
        if (contactName == "") {
            alert("Contact Name is required");
            $("contactname").focus();
            validate = false;
        }
        else if (contactno == "") { 
            alert("Contact Number is required.");
            $("#contactno").focus();
            validate = false;
        }
        return validate;
    }


    function getFavourite(response) { 

        var arr = JSON.parse(response);

        if (arr[0].result == "1"){ 
            window.location = "home.html"; 
            alert("Your favourite has been added.");
        }
        else { 
            alert("Unsuccessful");  

        }
    }