问chrome.runtime.sendMessage返回参数为undefined？

//background.js
chrome.runtime.onMessage.addListener(function (message, sender, sendResponse) {
   setTimeout(function(){
    if(message == "version"){  
         sendResponse('hi!');
     }
   },2000);
    
     return true;   
});
//content.js
var EXTENSION_ID = 'My_ExtensionID';
chrome.runtime.sendMessage(EXTENSION_ID, 'version', function (response) { 
        console.log(response); //undefined
}

//manifest.json
{
  "manifest_version": 2,
  "name": "My Cool Extension",
  "version": "0.1",
  "content_scripts": [ {
    "all_frames": true,
    "js": ["content.js" ],
    "matches": [ "http://*/*", "https://*/*", "file://*/*" ]
  } ],
  "permissions": [ "http://*/*", "https://*/*", "storage" ],
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}