如何在popup.js和background.js之间传递chrome扩展中的消息

Question

尝试开发chrome扩展以使用安全浏览查找API。想知道如何在popup.js和background.js之间发送消息（url，查找结果）。

这是popup.js

function myFunction() {
var url;
chrome.tabs.query(
                  {currentWindow: true, active: true},function(tabs){
                  url=tabs[0].url;

                  });
alert(url);
chrome.runtime.sendMessage({url: url}, function(response) {
                            document.getElementById("display").innerHTML=response.result;
                         //  alert(response.result);
                           });
}

window.addEventListener('DOMContentLoaded', myFunction);

这是background.js

 chrome.runtime.onMessage.addListener(
                                 function(request, sendResponse) {

                                 sendResponse({result: checkUrl(request.url)});
                                 });



function encode(str) {
    var s =  encodeURIComponent(str);


    s = s.replace('!','%21');
    s = s.replace('*','%2A');
    s = s.replace('(','%28');
    s = s.replace(')','%29');
    s = s.replace("'",'%27');


           return s;
}


var query = encode(url);

 var queryUrl = "https://sb-ssl.google.com/safebrowsing/api/lookup?        

client=CLIENT&key=AIzaSyDWNPq9LFwkQzwPl4D9EnCmYDgP7xVr5jY&appver=1.0&pver=3.1&url="+query;


function checkUrl(){

var xhr = new XMLHttpRequest();
xhr.open("GET", queryUrl, true);
xhr.onreadystatechange = function() {
if (xhr.readyState == 4) {
           //document.getElementById("safeBrowsing").innerText = xhr.responseText;
}
}
xhr.send();

return xhr.responseText;

}

清单

{
 "manifest_version": 2,
   "name": "secBrowsing",


 "description": "secure your browsing as you want",
  "version":"1.0",
  "background": {
    "scripts": ["background.js"]

 },
"browser_action":
{

 "default_popup":"popup.html" 

 },
"permissions":["tabs" ,"background"]
 }