sendMessage from popup to content.js not working in chrome extension

Question

I\'m trying to make a popup interface for a chrome extension. I can\'t seem to send a message from the popup.html/popup.js to the content.js script. Here\'s what I have so far.

Answer 1

I modified your popup.js and used DOMContentLoaded as Chrome extension suggested like:

popup.js:

 function popup() {
    chrome.tabs.query({currentWindow: true, active: true}, function (tabs){
    var activeTab = tabs[0];
    chrome.tabs.sendMessage(activeTab.id, {"message": "start"});
   });
}

document.addEventListener("DOMContentLoaded", function() {
  document.getElementById("button1").addEventListener("click", popup);
});

content.js:

chrome.runtime.onMessage.addListener(
      function(request, sender, sendResponse) {
        if( request.message === "start" ) {
         start();
             }
      }
    );

    function start(){
        alert("started");
    }

popup.html:

I've tested on my end it works.