increase Service Worker life time

I'm trying push notifications using service workers. use my own server to send notifications and eventSource is used to establish the connection. after i open the webpage service worker is running perfectly. but it stops after few seconds. what i want is to run service worker without getting stopped. i want it to run until the browser is opened. can anyone recommend a way to do that. ?

this is my ServiceWorker JS

/**
 * 
 */
'use strict';
var eventSource2 = new EventSource("Servlet");
console.log('Started', eventSource2);
eventSource2.addEventListener('install', function(event) {
    eventSource2.skipWaiting();
    console.log('Installed', event);

});

eventSource2.addEventListener('push',function(event) {
                    console.log(event.data);
                    var title = event.data;
                    self.registration.showNotification(title,{
                                        'body' : event.data,
                                        'icon' : 'http://icons.iconarchive.com/icons/designbolts/free-multimedia/1024/iMac-icon.png',
                                        'tag' : 'click',
                                    });
                    console.log("data from down", event.data);
                });

eventSource2.addEventListener('activate', function(event){
    console.log('Activated', event);
});

eventSource2.addEventListener('fetch', function(event) {
    console.log('Push message', event);
});