javascript - How to use navigator.onLine feature to POST from a form to a PHP? -

i trying use navigator.online check whether browser online or offline. if want post form html php based on condition, possible way so. below code same.

html

<script> var online = navigator.online; if(online){ function postdata() {       // 1. create xhr instance - start     var xhr;     if (window.xmlhttprequest) {         xhr = new xmlhttprequest();     }     else if (window.activexobject) {         xhr = new activexobject("msxml2.xmlhttp");     }     else {         throw new error("ajax not supported browser");     }     // 1. create xhr instance - end      // 2. define when xhr feed response server - start     xhr.onreadystatechange = function () {         if (xhr.readystate === 4) {             if (xhr.status == 200 && xhr.status < 300) {                 document.getelementbyid('div1').innerhtml = xhr.responsetext;             }         }     }     // 2. define when xhr feed response server - start      var userid = document.getelementbyid("userid").value;     var pid = document.getelementbyid("pid").value;     // var image = document.getelementbyid("image").value;     // 3. specify action, location , send server - start        xhr.open('post', 'login.php');     //xhr.open('post', 'config.php');     xhr.setrequestheader("content-type", "application/x-www-form-urlencoded");     xhr.send("userid=" + userid + "&pid=" + pid);     //xhr.send("&pid=" + pid);     // 3. specify action, location , send server - end  } } </script>