document.addEventListener('DOMContentLoaded', init);

function init(){
    var elem = document.getElementById('start');
    elem.addEventListener('click',func);
	var elem2 = document.getElementById('stop');
    elem2.addEventListener('click',func2); 
}

var first = true;

function func(){
	if(first == true){
		chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
			chrome.tabs.executeScript(null, {file:"jquery.js"});
			chrome.tabs.executeScript(null, {file:"script.js"});
		});
		first = false;
	}
	chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
		chrome.tabs.sendMessage(tabs[0].id, { greeting: "start" });
	});
}
function func2(){
	chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
		chrome.tabs.sendMessage(tabs[0].id, { greeting: "stop" });
	});
}